diff --git a/.gitignore b/.gitignore
index ac8828d1..24f54284 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,6 +9,8 @@ pkg
 .sass-cache
 .sassc
 .tmp
+graph.dot
+graph.jpg
 docs
 .rbenv-*
 .ruby-version
diff --git a/Gemfile.lock b/Gemfile.lock
index feae474c..bc35a7ad 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -26,6 +26,7 @@ PATH
       padrino-helpers (~> 0.13.0)
       parallel
       rack (>= 1.4.5, < 3)
+      rgl (~> 0.5.3)
       sass (>= 3.4)
       sassc (~> 2.0)
       servolux
@@ -113,6 +114,7 @@ GEM
     jaro_winkler (1.5.1)
     json (2.1.0)
     kramdown (1.17.0)
+    lazy_priority_queue (0.1.1)
     libv8 (6.7.288.46.1)
     liquid (4.0.1)
     listen (3.1.5)
@@ -166,6 +168,9 @@ GEM
     rb-inotify (0.10.0)
       ffi (~> 1.0)
     redcarpet (3.4.0)
+    rgl (0.5.3)
+      lazy_priority_queue (~> 0.1.0)
+      stream (~> 0.5.0)
     rspec (3.8.0)
       rspec-core (~> 3.8.0)
       rspec-expectations (~> 3.8.0)
@@ -215,6 +220,7 @@ GEM
     slim (4.0.1)
       temple (>= 0.7.6, < 0.9)
       tilt (>= 2.0.6, < 2.1)
+    stream (0.5)
     stylus (1.0.2)
       execjs
       stylus-source
diff --git a/middleman-cli/lib/middleman-cli/build.rb b/middleman-cli/lib/middleman-cli/build.rb
index 65c088e3..204ba6f3 100644
--- a/middleman-cli/lib/middleman-cli/build.rb
+++ b/middleman-cli/lib/middleman-cli/build.rb
@@ -44,6 +44,10 @@ module Middleman::Cli
                  type: :boolean,
                  default: false,
                  desc: 'Track file dependencies'
+    class_option :visualize_graph,
+                 type: :boolean,
+                 default: false,
+                 desc: 'Generate a visual of the dependency graph'
     class_option :only_changed,
                  type: :boolean,
                  default: false,
@@ -95,7 +99,8 @@ module Middleman::Cli
                                          parallel: options['parallel'],
                                          only_changed: options['only_changed'],
                                          missing_and_changed: missing_and_changed,
-                                         track_dependencies: should_track_dependencies)
+                                         track_dependencies: should_track_dependencies,
+                                         visualize_graph: options['visualize_graph'])
         builder.thor = self
         builder.on_build_event(&method(:on_event))
       end
diff --git a/middleman-core/features/incremental_builds.feature b/middleman-core/features/incremental_builds.feature
new file mode 100644
index 00000000..511d9f3b
--- /dev/null
+++ b/middleman-core/features/incremental_builds.feature
@@ -0,0 +1,174 @@
+Feature: Incremental builds
+
+  Scenario: Changing a page should only rebuild that page
+    Given an empty app
+    When a file named "config.rb" with:
+      """
+      """
+    When a file named "source/standalone.html.erb" with:
+      """
+      Initial
+      """
+    When a file named "source/other.html.erb" with:
+      """
+      Some other file
+      """
+    Then build the app tracking dependencies
+    Then the output should contain "create  build/standalone.html"
+    Then the following files should exist:
+      | build/standalone.html |
+    And the file "build/standalone.html" should contain "Initial"
+    When a file named "source/standalone.html.erb" with:
+      """
+      Updated
+      """
+    Then build app with only changed
+    Then there are "0" files which are "      create  "
+    Then there are "1" files which are "     updated  "
+    Then the output should contain "updated  build/standalone.html"
+    Then the following files should exist:
+      | build/standalone.html |
+    And the file "build/standalone.html" should contain "Updated"
+
+  Scenario: Changing a layout should only rebuild pages which use that layout
+    Given an empty app
+    When a file named "config.rb" with:
+      """
+      """
+    When a file named "source/layout.erb" with:
+      """
+      Initial
+      <%= yield %>
+      """
+    When a file named "source/page1.html.erb" with:
+      """
+      Page 1
+      """
+    When a file named "source/page2.html.erb" with:
+      """
+      Page 2
+      """
+    When a file named "source/no-layout.html.erb" with:
+      """
+      ---
+      layout: false
+      ---
+
+      Another page
+      """
+    Then build the app tracking dependencies
+    Then the output should contain "create  build/page1.html"
+    Then the output should contain "create  build/page2.html"
+    Then the following files should exist:
+      | build/page1.html |
+      | build/page2.html |
+    And the file "build/page1.html" should contain "Initial"
+    And the file "build/page1.html" should contain "Page 1"
+    And the file "build/page2.html" should contain "Initial"
+    And the file "build/page2.html" should contain "Page 2"
+    When a file named "source/layout.erb" with:
+      """
+      Updated
+      <%= yield %>
+      """
+    Then build app with only changed
+    Then there are "0" files which are "      create  "
+    Then there are "2" files which are "     updated  "
+    Then the output should contain "updated  build/page1.html"
+    Then the output should contain "updated  build/page2.html"
+    Then the following files should exist:
+      | build/page1.html |
+      | build/page2.html |
+    And the file "build/page1.html" should contain "Updated"
+    And the file "build/page1.html" should contain "Page 1"
+    And the file "build/page2.html" should contain "Updated"
+    And the file "build/page2.html" should contain "Page 2"
+
+  Scenario: Changing a piece of data only rebuilds the pages which use it
+    Given an empty app
+    When a file named "config.rb" with:
+      """
+      data.people.each do |p|
+        proxy "/person-#{p.slug}.html", '/person.html', ignore: true, locals: { person: p }
+      end
+      """
+    When a file named "data/people.yml" with:
+      """
+      -
+        slug: "one"
+        name: "Person One"
+        age: 5
+      -
+        slug: "two"
+        name: "Person Two"
+        age: 10
+      """
+    When a file named "source/person.html.erb" with:
+      """
+      <%= person.name %>
+      """
+    Then build the app tracking dependencies
+    Then the output should contain "create  build/person-one.html"
+    Then the output should contain "create  build/person-two.html"
+    Then the following files should exist:
+      | build/person-one.html   |
+      | build/person-two.html   |
+    And the file "build/person-one.html" should contain "Person One"
+    And the file "build/person-two.html" should contain "Person Two"
+    When a file named "data/people.yml" with:
+      """
+      -
+        slug: "one"
+        name: "Person One"
+        age: 15
+      -
+        slug: "two"
+        name: "Person Two"
+        age: 20
+      """
+    Then build app with only changed
+    Then there are "0" files which are "      create  "
+    Then there are "0" files which are "     updated  "
+    Then the following files should exist:
+      | build/person-one.html   |
+      | build/person-two.html   |
+    When a file named "data/people.yml" with:
+      """
+      -
+        slug: "one"
+        name: "Person One"
+        age: 5
+      -
+        slug: "two"
+        name: "Person Updated"
+        age: 10
+      """
+    Then build app with only changed
+    Then there are "0" files which are "      create  "
+    Then there are "1" files which are "     updated  "
+    Then the output should contain "updated  build/person-two.html"
+    Then the following files should exist:
+      | build/person-one.html   |
+      | build/person-two.html   |
+    And the file "build/person-two.html" should contain "Person Updated"
+    When a file named "data/people.yml" with:
+      """
+      -
+        slug: "updated-slug"
+        name: "Person New Slug"
+        age: 5
+      -
+        slug: "two"
+        name: "Person Updated"
+        age: 10
+      """
+    Then build app with only changed
+    Then there are "1" files which are "      create  "
+    Then there are "1" files which are "      remove  "
+    Then there are "0" files which are "     updated  "
+    Then the output should contain "create  build/person-updated-slug.html"
+    Then the output should contain "remove  build/person-one.html"
+    Then the following files should exist:
+      | build/person-updated-slug.html |
+      | build/person-two.html   |
+    And the file "build/person-updated-slug.html" should contain "Person New Slug"
\ No newline at end of file
diff --git a/middleman-core/fixtures/data-app/data/pages.yml b/middleman-core/fixtures/data-app/data/pages.yml
index 18f63665..0cd5973b 100644
--- a/middleman-core/fixtures/data-app/data/pages.yml
+++ b/middleman-core/fixtures/data-app/data/pages.yml
@@ -1,12 +1,16 @@
 -
   from: "/test1.html"
   to:   "/index.html"
+  guid: 0
 -
   from: "/test2.html"
   to:   "/index.html"
+  guid: 1
 -
   from: "/test3.html"
   to:   "/index.html"
+  guid: 2
 -
   from: "/test4.html"
-  to:   "/index.html"
\ No newline at end of file
+  to:   "/index.html"
+  guid: 3
\ No newline at end of file
diff --git a/middleman-core/fixtures/data-app/source/first.html.erb b/middleman-core/fixtures/data-app/source/first.html.erb
new file mode 100644
index 00000000..70c600c4
--- /dev/null
+++ b/middleman-core/fixtures/data-app/source/first.html.erb
@@ -0,0 +1,3 @@
+<%= data.pages.first %>
+<%#= data.pages.first(2) %>
+<%#= data.pages.first(2).first %>
\ No newline at end of file
diff --git a/middleman-core/fixtures/data-app/source/index.html.erb b/middleman-core/fixtures/data-app/source/index.html.erb
index 4cd6464e..f47aba51 100755
--- a/middleman-core/fixtures/data-app/source/index.html.erb
+++ b/middleman-core/fixtures/data-app/source/index.html.erb
@@ -1,10 +1 @@
-<h1>Welcome</h1>
-
-
-<%= data.pages.first %>
-<%= data.pages.first(2) %>
-<%= data.pages.first(2).first %>
---
-<%= data.pages.last %>
-<%= data.pages.last(2) %>
-<%= data.pages.last(2).last %>
\ No newline at end of file
+<h1>Welcome</h1>
\ No newline at end of file
diff --git a/middleman-core/fixtures/data-app/source/last.html.erb b/middleman-core/fixtures/data-app/source/last.html.erb
new file mode 100644
index 00000000..e42a594e
--- /dev/null
+++ b/middleman-core/fixtures/data-app/source/last.html.erb
@@ -0,0 +1,3 @@
+<%= data.pages.last %>
+<%#= data.pages.last(2) %>
+<%#= data.pages.last(2).last %>
\ No newline at end of file
diff --git a/middleman-core/fixtures/data-app/source/layout.erb b/middleman-core/fixtures/data-app/source/layout.erb
index 0520e80c..764e2955 100644
--- a/middleman-core/fixtures/data-app/source/layout.erb
+++ b/middleman-core/fixtures/data-app/source/layout.erb
@@ -1,5 +1,6 @@
 <html>
   <body>
+    <%#= data.pages[1].guid %>
     <%= yield %>
   </body>
 </html>
\ No newline at end of file
diff --git a/middleman-core/fixtures/data-app/source/no-layout.html.erb b/middleman-core/fixtures/data-app/source/no-layout.html.erb
new file mode 100644
index 00000000..7469e6ea
--- /dev/null
+++ b/middleman-core/fixtures/data-app/source/no-layout.html.erb
@@ -0,0 +1,5 @@
+---
+layout: false
+---
+
+No layout
\ No newline at end of file
diff --git a/middleman-core/fixtures/data-app/source/random b/middleman-core/fixtures/data-app/source/random
new file mode 100644
index 00000000..e69de29b
diff --git a/middleman-core/fixtures/data-app/source/two.html.erb b/middleman-core/fixtures/data-app/source/two.html.erb
new file mode 100644
index 00000000..d8263ee9
--- /dev/null
+++ b/middleman-core/fixtures/data-app/source/two.html.erb
@@ -0,0 +1 @@
+2
\ No newline at end of file
diff --git a/middleman-core/fixtures/data-path-dependency-app/config.rb b/middleman-core/fixtures/data-path-dependency-app/config.rb
deleted file mode 100644
index 16ee9410..00000000
--- a/middleman-core/fixtures/data-path-dependency-app/config.rb
+++ /dev/null
@@ -1,3 +0,0 @@
-data.people.each do |p|
-  proxy "/#{p.slug}.html", '/person.html', ignore: true, locals: { person: p }
-end
diff --git a/middleman-core/fixtures/incremental-build-app/config.rb b/middleman-core/fixtures/incremental-build-app/config.rb
new file mode 100644
index 00000000..98c47ee9
--- /dev/null
+++ b/middleman-core/fixtures/incremental-build-app/config.rb
@@ -0,0 +1,3 @@
+# data.people.each do |p|
+#   proxy "/#{p.slug}.html", '/person.html', ignore: true, locals: { person: p }
+# end
diff --git a/middleman-core/fixtures/data-path-dependency-app/data/people.yml b/middleman-core/fixtures/incremental-build-app/data/people.yml
similarity index 100%
rename from middleman-core/fixtures/data-path-dependency-app/data/people.yml
rename to middleman-core/fixtures/incremental-build-app/data/people.yml
diff --git a/middleman-core/fixtures/data-path-dependency-app/source/person.html.erb b/middleman-core/fixtures/incremental-build-app/source/person.html.erb
similarity index 100%
rename from middleman-core/fixtures/data-path-dependency-app/source/person.html.erb
rename to middleman-core/fixtures/incremental-build-app/source/person.html.erb
diff --git a/middleman-core/lib/middleman-core/builder.rb b/middleman-core/lib/middleman-core/builder.rb
index 308e2b3b..664c3f1c 100644
--- a/middleman-core/lib/middleman-core/builder.rb
+++ b/middleman-core/lib/middleman-core/builder.rb
@@ -40,6 +40,7 @@ module Middleman
       @only_changed = options_hash.fetch(:only_changed, false)
       @missing_and_changed = options_hash.fetch(:missing_and_changed, false)
       @track_dependencies = options_hash.fetch(:track_dependencies, false)
+      @visualize_graph = @track_dependencies && options_hash.fetch(:visualize_graph, false)
       @dry_run = options_hash.fetch(:dry_run)
       @cleaning = !@dry_run && options_hash.fetch(:clean)
 
@@ -94,7 +95,7 @@ module Middleman
         prerender_css.tap do |resources|
           if @track_dependencies
             resources.each do |r|
-              @graph.add_edge(r[1]) unless r[1].nil?
+              @graph.add_edge_set(r[1]) unless r[1].nil?
             end
           end
         end
@@ -106,7 +107,7 @@ module Middleman
         output_files.tap do |resources|
           if @track_dependencies
             resources.each do |r|
-              @graph.add_edge(r[1]) unless r[1].nil?
+              @graph.add_edge_set(r[1]) unless r[1].nil?
             end
           end
         end
@@ -115,9 +116,12 @@ module Middleman
       ::Middleman::Profiling.report('build')
 
       unless @has_error
-        partial_update_with_no_changes = (@only_changed || @missing_and_changed) && !@invalidated_files.empty?
+        partial_update_with_no_changes = (@only_changed || @missing_and_changed) && @invalidated_files.empty?
+
         ::Middleman::Dependencies.serialize_and_save(@app, @graph) if @track_dependencies && !partial_update_with_no_changes
 
+        ::Middleman::Dependencies.visualize_graph(@app, @graph) if @track_dependencies && @visualize_graph
+
         ::Middleman::Util.instrument 'builder.clean' do
           clean! if @cleaning
         end
@@ -326,12 +330,11 @@ module Middleman
           else
             content = resource.render({}, {})
 
-            unless resource.vertices.empty?
-              vertices = ::Middleman::Dependencies::Edge.new(
-                ::Middleman::Dependencies::FileVertex.from_resource(resource),
-                resource.vertices
-              )
-            end
+            self_vertex = ::Middleman::Dependencies::FileVertex.from_resource(resource)
+            vertices = ::Middleman::Dependencies::Edge.new(
+              self_vertex,
+              resource.vertices << self_vertex
+            )
 
             export_file!(output_file, binary_encode(content))
           end
diff --git a/middleman-core/lib/middleman-core/core_extensions/data/controller.rb b/middleman-core/lib/middleman-core/core_extensions/data/controller.rb
index e59f5df3..91c822a8 100644
--- a/middleman-core/lib/middleman-core/core_extensions/data/controller.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/data/controller.rb
@@ -47,12 +47,6 @@ module Middleman
           end
         end
 
-        def vertices_for_key(k)
-          @data_stores.reduce(::Hamster::Set.empty) do |sum, s|
-            sum | s.vertices_for_key(k)
-          end
-        end
-
         def enhanced_data(k)
           value = key(k)
 
diff --git a/middleman-core/lib/middleman-core/core_extensions/data/proxies/array.rb b/middleman-core/lib/middleman-core/core_extensions/data/proxies/array.rb
index f1b74c2a..12672bd4 100644
--- a/middleman-core/lib/middleman-core/core_extensions/data/proxies/array.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/data/proxies/array.rb
@@ -54,10 +54,12 @@ module Middleman
           end
 
           def to_s
+            log_access(:__full_access__)
             @data.to_s
           end
 
           def to_json
+            log_access(:__full_access__)
             @data.to_a.to_json
           end
 
diff --git a/middleman-core/lib/middleman-core/core_extensions/data/proxies/hash.rb b/middleman-core/lib/middleman-core/core_extensions/data/proxies/hash.rb
index bdc21164..bfa4ae8f 100644
--- a/middleman-core/lib/middleman-core/core_extensions/data/proxies/hash.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/data/proxies/hash.rb
@@ -23,10 +23,12 @@ module Middleman
           end
 
           def to_s
+            log_access(:__full_access__)
             @data.to_s
           end
 
           def to_json
+            log_access(:__full_access__)
             @data.to_h.to_json
           end
         end
diff --git a/middleman-core/lib/middleman-core/core_extensions/data/stores/base.rb b/middleman-core/lib/middleman-core/core_extensions/data/stores/base.rb
index 1a2ac5d9..5edb7901 100644
--- a/middleman-core/lib/middleman-core/core_extensions/data/stores/base.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/data/stores/base.rb
@@ -29,11 +29,6 @@ module Middleman
             Hamster::Set.empty
           end
 
-          Contract Symbol => ImmutableSetOf[::Middleman::Dependencies::Vertex]
-          def vertices_for_key(_k)
-            Hamster::Set.empty
-          end
-
           Contract Hash
           def to_h
             keys.each_with_object({}) do |k, sum|
diff --git a/middleman-core/lib/middleman-core/core_extensions/data/stores/in_memory.rb b/middleman-core/lib/middleman-core/core_extensions/data/stores/in_memory.rb
index cd92272b..246e319f 100644
--- a/middleman-core/lib/middleman-core/core_extensions/data/stores/in_memory.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/data/stores/in_memory.rb
@@ -27,11 +27,6 @@ module Middleman
             Hamster::Set.new(@keys_to_vertex.values.flatten(1))
           end
 
-          Contract Symbol => ImmutableSetOf[::Middleman::Dependencies::Vertex]
-          def vertices_for_key(k)
-            @keys_to_vertex[k] || ::Hamster::Set.empty
-          end
-
           # Store static data hash
           #
           # @param [Symbol] name Name of the data, used for namespacing
diff --git a/middleman-core/lib/middleman-core/core_extensions/data/stores/local_file.rb b/middleman-core/lib/middleman-core/core_extensions/data/stores/local_file.rb
index e7a9bdb2..4461a731 100644
--- a/middleman-core/lib/middleman-core/core_extensions/data/stores/local_file.rb
+++ b/middleman-core/lib/middleman-core/core_extensions/data/stores/local_file.rb
@@ -26,12 +26,6 @@ module Middleman
 
             @app = app
             @local_data = {}
-            @paths_to_vertex = {}
-          end
-
-          Contract Symbol => ImmutableSetOf[::Middleman::Dependencies::Vertex]
-          def vertices_for_key(k)
-            @paths_to_vertex[k] || ::Hamster::Set.empty
           end
 
           Contract ArrayOf[IsA['Middleman::SourceFile']], ArrayOf[IsA['Middleman::SourceFile']] => Any
@@ -69,16 +63,6 @@ module Middleman
               data_branch = data_branch[dir.to_sym]
             end
 
-            # For now, all files nested under a folder in `data/` will invalidate
-            # the whole folder.
-            if paths.empty?
-              @paths_to_vertex[basename.to_sym] ||= ::Hamster::Set.empty
-              @paths_to_vertex[basename.to_sym] <<= ::Middleman::Dependencies::FileVertex.from_source_file(@app, file)
-            else
-              @paths_to_vertex[paths.first.to_sym] ||= ::Hamster::Set.empty
-              @paths_to_vertex[paths.first.to_sym] <<= ::Middleman::Dependencies::FileVertex.from_source_file(@app, file)
-            end
-
             data_branch[basename.to_sym] = data
           end
 
diff --git a/middleman-core/lib/middleman-core/data_proxy.rb b/middleman-core/lib/middleman-core/data_proxy.rb
index fc471848..4fa98649 100644
--- a/middleman-core/lib/middleman-core/data_proxy.rb
+++ b/middleman-core/lib/middleman-core/data_proxy.rb
@@ -56,11 +56,7 @@ module Middleman
     end
 
     def method_missing(method, *args, &block)
-      if @ctx.internal_data_store.key?(method)
-        @ctx.vertices |= @ctx.internal_data_store.vertices_for_key(method)
-
-        return @ctx.internal_data_store.proxied_data(method, self)
-      end
+      return @ctx.internal_data_store.proxied_data(method, self) if @ctx.internal_data_store.key?(method)
 
       super
     end
diff --git a/middleman-core/lib/middleman-core/dependencies.rb b/middleman-core/lib/middleman-core/dependencies.rb
index 8930288c..b8ba8441 100644
--- a/middleman-core/lib/middleman-core/dependencies.rb
+++ b/middleman-core/lib/middleman-core/dependencies.rb
@@ -24,8 +24,16 @@ module Middleman
       end
     end
 
+    Contract IsA['::Middleman::Application'], Graph => Any
+    def visualize_graph(_app, graph)
+      require 'rgl/dot'
+      graph.graph.write_to_graphic_file('jpg', 'graph')
+    end
+
     Contract IsA['::Middleman::Application'], Graph => String
     def serialize(app, graph)
+      serialized = graph.serialize
+
       ruby_files = Dir.glob(RUBY_FILES).reduce([]) do |sum, file|
         sum << {
           file: Pathname(File.expand_path(file)).relative_path_from(app.root_path).to_s,
@@ -33,21 +41,10 @@ module Middleman
         }
       end
 
-      edges = graph.dependency_map.reduce([]) do |sum, (vertex, depended_on_by)|
-        sum << {
-          key: vertex.key,
-          depended_on_by: depended_on_by.delete(vertex).to_a.map(&:key).sort
-        }
-      end
-
-      vertices = graph.dependency_map.reduce([]) do |sum, (vertex, _depended_on_by)|
-        sum << vertex.serialize
-      end
-
       ::YAML.dump(
-        ruby_files: ruby_files.sort_by { |d| d[:file] },
-        edges: edges.sort_by { |d| d[:key] },
-        vertices: vertices.sort_by { |d| d[:key] }
+        {
+          ruby_files: ruby_files.sort_by { |d| d[:file] }
+        }.merge(serialized)
       )
     end
 
@@ -105,17 +102,18 @@ module Middleman
         end
       end
 
-      graph = Graph.new(vertices)
+      graph = Graph.new
+      vertices.values.each { |v| graph.add_vertex(v) }
 
-      Contract ImmutableHashOf[Vertex, ImmutableSetOf[Vertex]]
-
-      edges = data[:edges]
-      graph.dependency_map = edges.reduce(::Hamster::Hash.empty) do |sum, row|
-        vertex = graph.vertices[row[:key]]
-        depended_on_by = row[:depended_on_by].map { |k| graph.vertices[k] }
-        sum.put(vertex, ::Hamster::Set.new(depended_on_by) << vertex)
+      data[:edges].each do |e|
+        graph.add_edge_by_key(e[:depends_on], e[:key])
       end
 
+      graph.invalidate_changes!
+
+      # require 'rgl/dot'
+      # graph.graph.write_to_graphic_file('jpg', 'valid')
+
       graph
     rescue StandardError
       raise InvalidDepsYAML
diff --git a/middleman-core/lib/middleman-core/dependencies/graph.rb b/middleman-core/lib/middleman-core/dependencies/graph.rb
index 599cc196..2d1af09c 100644
--- a/middleman-core/lib/middleman-core/dependencies/graph.rb
+++ b/middleman-core/lib/middleman-core/dependencies/graph.rb
@@ -1,87 +1,121 @@
 require 'set'
+require 'rgl/adjacency'
 require 'middleman-core/contracts'
 require 'middleman-core/dependencies/vertices/vertex'
 require 'middleman-core/dependencies/edge'
 
 module Middleman
   module Dependencies
+    class DirectedAdjacencyGraph < ::RGL::DirectedAdjacencyGraph
+      def add_vertex(v)
+        super(merged_vertex_or_new(v))
+      end
+
+      def add_edge(u, v)
+        super(merged_vertex_or_new(u), merged_vertex_or_new(v))
+      end
+
+      def remove_vertex(vertex)
+        each_adjacent(vertex) do |v|
+          remove_vertex(v) unless v == vertex
+        end
+
+        super(vertex)
+      end
+
+      def find_vertex_by_key(key)
+        vertices.find { |v| v.key == key }
+      end
+
+      protected
+
+      def merged_vertex_or_new(vertex)
+        found_vertex = find_vertex_by_key(vertex.key)
+
+        if found_vertex
+          found_vertex.merge!(vertex)
+          found_vertex
+        else
+          vertex
+        end
+      end
+    end
+
     class Graph
       include Contracts
 
-      Contract HashOf[Vertex::VERTEX_KEY, Vertex]
-      attr_reader :vertices
+      Contract DirectedAdjacencyGraph
+      attr_reader :graph
 
-      Contract ImmutableHashOf[Vertex, ImmutableSetOf[Vertex]]
-      attr_accessor :dependency_map
-
-      def initialize(vertices = {})
-        @vertices = vertices
-        @dependency_map = ::Hamster::Hash.empty
+      def initialize(_vertices = {})
+        @graph = DirectedAdjacencyGraph.new
       end
 
-      Contract Vertex => Vertex
-      def merged_vertex_or_new(v)
-        if @vertices[v.key]
-          @vertices[v.key].merge!(v)
-        else
-          @vertices[v.key] = v
-        end
+      def invalidate_vertex!(vertex)
+        @graph.remove_vertex(vertex)
+      end
 
-        @vertices[v.key]
+      Contract Vertex => Any
+      def add_vertex(vertex)
+        @graph.add_vertex(vertex)
+      end
+
+      Contract Vertex, Vertex => Any
+      def add_edge(source, target)
+        if source == target
+          add_vertex(source)
+        else
+          @graph.add_edge(source, target)
+        end
+      end
+
+      Contract Symbol, Symbol => Any
+      def add_edge_by_key(source, target)
+        a = @graph.find_vertex_by_key(source)
+        b = @graph.find_vertex_by_key(target)
+
+        add_edge(a, b)
       end
 
       Contract Edge => Any
-      def add_edge(edge)
-        deduped_vertex = merged_vertex_or_new edge.vertex
-
-        # FIXME
-        # Depending on yourself (<< deduped_vertex)
-        # is only useful for files in source/ that can be depended on and also
-        # be their own route
-        @dependency_map = @dependency_map.put(deduped_vertex) do |v|
-          (v || ::Hamster::Set.empty) << deduped_vertex
-        end
-
+      def add_edge_set(edge)
         return if edge.depends_on.nil?
 
         edge.depends_on.each do |depended_on|
-          deduped_depended_on = merged_vertex_or_new depended_on
-
-          @dependency_map = @dependency_map.put(deduped_depended_on) do |v|
-            (v || ::Hamster::Set.empty) << deduped_depended_on << deduped_vertex
-          end
+          add_edge(depended_on, edge.vertex)
         end
       end
 
-      Contract String => Bool
-      def exists?(file_path)
-        @dependency_map.key?(file_path)
+      def serialize
+        edges = @graph.edges.map do |edge|
+          {
+            key: edge.target.key,
+            depends_on: edge.source.key
+          }
+        end
+
+        vertices = @graph.vertices.map(&:serialize)
+
+        {
+          edges: edges.sort_by { |d| [d[:key], d[:depends_on]] },
+          vertices: vertices.sort_by { |d| d[:key] }
+        }
+      end
+
+      Contract Any
+      def invalidate_changes!
+        @invalidated = @graph.vertices.reject(&:valid?)
+        @invalidated.each { |v| @graph.remove_vertex(v) }
       end
 
       Contract ImmutableSetOf[Vertex]
       def invalidated
-        @_invalidated_cache ||= begin
-          invalidated_vertices = @dependency_map.keys.select do |vertex|
-            # Either "Missing from known vertices"
-            # Or invalided by the class
-            !@vertices.key?(vertex.key) || !vertex.valid?
-          end
-
-          invalidated_vertices.reduce(::Hamster::Set.empty) do |sum, vertex|
-            sum | invalidated_with_parents(vertex)
-          end
-        end
-      end
-
-      Contract Vertex => ImmutableSetOf[Vertex]
-      def invalidated_with_parents(vertex)
-        # TODO, recurse more?
-        @dependency_map[vertex] << vertex
+        ::Hamster::Set.new(@invalidated)
       end
 
       Contract IsA['::Middleman::Sitemap::Resource'] => Bool
       def invalidates_resource?(resource)
-        invalidated.any? { |d| d.invalidates_resource?(resource) }
+        @graph.vertices.none? { |d| d.matches_resource?(resource) }
       end
     end
   end
diff --git a/middleman-core/lib/middleman-core/dependencies/vertices/file_vertex.rb b/middleman-core/lib/middleman-core/dependencies/vertices/file_vertex.rb
index b56a68de..45cd4d04 100644
--- a/middleman-core/lib/middleman-core/dependencies/vertices/file_vertex.rb
+++ b/middleman-core/lib/middleman-core/dependencies/vertices/file_vertex.rb
@@ -38,7 +38,7 @@ module Middleman
       end
 
       Contract IsA['Middleman::Sitemap::Resource'] => Bool
-      def invalidates_resource?(resource)
+      def matches_resource?(resource)
         resource.file_descriptor[:full_path].to_s == @full_path
       end
 
diff --git a/middleman-core/lib/middleman-core/dependencies/vertices/vertex.rb b/middleman-core/lib/middleman-core/dependencies/vertices/vertex.rb
index 10655742..ac72de1f 100644
--- a/middleman-core/lib/middleman-core/dependencies/vertices/vertex.rb
+++ b/middleman-core/lib/middleman-core/dependencies/vertices/vertex.rb
@@ -42,7 +42,7 @@ module Middleman
       end
 
       Contract IsA['Middleman::Sitemap::Resource'] => Bool
-      def invalidates_resource?(_resource)
+      def matches_resource?(_resource)
         false
       end
 
diff --git a/middleman-core/lib/middleman-core/step_definitions/builder_steps.rb b/middleman-core/lib/middleman-core/step_definitions/builder_steps.rb
index a111ca8e..ee0d8fad 100644
--- a/middleman-core/lib/middleman-core/step_definitions/builder_steps.rb
+++ b/middleman-core/lib/middleman-core/step_definitions/builder_steps.rb
@@ -6,21 +6,27 @@ end
 
 Given /^a built app at "([^\"]*)"$/ do |path|
   step %(a fixture app "#{path}")
+  step %(I run `middleman build --verbose --no-parallel`)
+end
 
-  cwd = File.expand_path(aruba.current_directory)
-  step %(I set the environment variable "MM_ROOT" to "#{cwd}")
+Then /^build the app tracking dependencies$/ do
+  step %(I run `middleman build --track-dependencies --no-parallel`)
+  step %(was successfully built)
+end
 
-  step %(I run `middleman build --verbose`)
+Then /^build app with only changed$/ do
+  step %(I run `middleman build --track-dependencies --only-changed --no-parallel`)
+  step %(was successfully built)
 end
 
 Given /^was successfully built$/ do
-  # step %(the output should contain "Project built successfully.")
+  step %(the output should contain "Project built successfully.")
   step %(the exit status should be 0)
   step %(a directory named "build" should exist)
 end
 
 Given /^was not successfully built$/ do
-  # step %(the output should not contain "Project built successfully.")
+  step %(the output should not contain "Project built successfully.")
   step %(the exit status should not be 0)
   step %(a directory named "build" should not exist)
 end
@@ -36,7 +42,7 @@ Given /^a built app at "([^\"]*)" with flags "([^\"]*)"$/ do |path, flags|
   cwd = File.expand_path(aruba.current_directory)
   step %(I set the environment variable "MM_ROOT" to "#{cwd}")
 
-  step %(I run `middleman build #{flags}`)
+  step %(I run `middleman build --no-parallel #{flags}`)
 end
 
 Given /^a successfully built app at "([^\"]*)" with flags "([^\"]*)"$/ do |path, flags|
@@ -55,3 +61,8 @@ Given /^I run the interactive middleman server$/ do
   step %(I set the environment variable "MM_ROOT" to "#{cwd}")
   step %(I run `middleman server` interactively)
 end
+
+Then('there are {string} files which are {string}') do |num, str|
+  # $stderr.puts last_command_started.output
+  expect(last_command_started.output.scan(str).length).to be num.to_i
+end
diff --git a/middleman-core/lib/middleman-core/step_definitions/middleman_steps.rb b/middleman-core/lib/middleman-core/step_definitions/middleman_steps.rb
index 7b51a111..41dc57ce 100644
--- a/middleman-core/lib/middleman-core/step_definitions/middleman_steps.rb
+++ b/middleman-core/lib/middleman-core/step_definitions/middleman_steps.rb
@@ -7,9 +7,17 @@ Given /^app "([^\"]*)" is using config "([^\"]*)"$/ do |_path, config_name|
 end
 
 Given /^an empty app$/ do
+  ENV['MM_ROOT'] = nil
+
+  # This step can be reentered from several places but we don't want
+  # to keep re-copying and re-cd-ing into ever-deeper directories
+  next if File.basename(expand_path('.')) == 'empty_app'
+
   step %(a directory named "empty_app")
   step %(I cd to "empty_app")
-  ENV['MM_ROOT'] = nil
+
+  cwd = File.expand_path(aruba.current_directory)
+  step %(I set the environment variable "MM_ROOT" to "#{cwd}")
 end
 
 Given /^a fixture app "([^\"]*)"$/ do |path|
@@ -25,6 +33,9 @@ Given /^a fixture app "([^\"]*)"$/ do |path|
   FileUtils.cp_r(target_path, expand_path('.'))
 
   step %(I cd to "#{path}")
+
+  cwd = File.expand_path(aruba.current_directory)
+  step %(I set the environment variable "MM_ROOT" to "#{cwd}")
 end
 
 Then /^the file "([^\"]*)" has the contents$/ do |path, contents|
diff --git a/middleman-core/middleman-core.gemspec b/middleman-core/middleman-core.gemspec
index 232688e1..5bee8451 100644
--- a/middleman-core/middleman-core.gemspec
+++ b/middleman-core/middleman-core.gemspec
@@ -26,6 +26,7 @@ Gem::Specification.new do |s|
   s.add_dependency('parallel')
   s.add_dependency('servolux')
   s.add_dependency('dotenv')
+  s.add_dependency('rgl', ['~> 0.5.3'])
 
   # Helpers
   s.add_dependency('activesupport', ['>= 4.2', '< 5.2'])