diff --git a/actionview/CHANGELOG.md b/actionview/CHANGELOG.md
index a1e94384bd..bcbd3d1387 100644
--- a/actionview/CHANGELOG.md
+++ b/actionview/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Add support for conditional values to TagBuilder.
+
+    *Joel Hawksley*
+
 *   Fix `select_tag` so that it doesn't change `options` when `include_blank` is present.
 
     *Younes SERRAJ*
diff --git a/actionview/lib/action_view/helpers/tag_helper.rb b/actionview/lib/action_view/helpers/tag_helper.rb
index 3979721d34..123da36c3f 100644
--- a/actionview/lib/action_view/helpers/tag_helper.rb
+++ b/actionview/lib/action_view/helpers/tag_helper.rb
@@ -85,7 +85,9 @@ module ActionView
         end
 
         def tag_option(key, value, escape)
-          if value.is_a?(Array)
+          case value
+          when Array, Hash
+            value = build_tag_values(value)
             value = escape ? safe_join(value, " ") : value.join(" ")
           else
             value = escape ? ERB::Util.unwrapped_html_escape(value) : value.to_s.dup
@@ -95,6 +97,26 @@ module ActionView
         end
 
         private
+
+          def build_tag_values(*args)
+            tag_values = []
+
+            args.each do |tag_value|
+              case tag_value
+              when String
+                tag_values << tag_value if tag_value.present?
+              when Hash
+                tag_value.each do |key, val|
+                  tag_values << key if val
+                end
+              when Array
+                tag_values << build_tag_values(*tag_value).presence
+              end
+            end
+
+            tag_values.compact.flatten
+          end
+
           def prefix_tag_option(prefix, key, value, escape)
             key = "#{prefix}-#{key.to_s.dasherize}"
             unless value.is_a?(String) || value.is_a?(Symbol) || value.is_a?(BigDecimal)
@@ -233,6 +255,9 @@ module ActionView
       #
       #   tag("div", data: { name: 'Stephen', city_state: %w(Chicago IL) })
       #   # => <div data-name="Stephen" data-city-state="[&quot;Chicago&quot;,&quot;IL&quot;]" />
+      #
+      #   tag("div", class: { highlight: current_user.admin? })
+      #   # => <div class="highlight" />
       def tag(name = nil, options = nil, open = false, escape = true)
         if name.nil?
           tag_builder
@@ -260,6 +285,8 @@ module ActionView
       #    # => <div class="strong"><p>Hello world!</p></div>
       #   content_tag(:div, "Hello world!", class: ["strong", "highlight"])
       #    # => <div class="strong highlight">Hello world!</div>
+      #   content_tag(:div, "Hello world!", class: ["strong", { highlight: current_user.admin? }])
+      #    # => <div class="strong highlight">Hello world!</div>
       #   content_tag("select", options, multiple: true)
       #    # => <select multiple="multiple">...options...</select>
       #
diff --git a/actionview/test/template/tag_helper_test.rb b/actionview/test/template/tag_helper_test.rb
index 9a6226fd04..1dc27fe20c 100644
--- a/actionview/test/template/tag_helper_test.rb
+++ b/actionview/test/template/tag_helper_test.rb
@@ -239,6 +239,68 @@ class TagHelperTest < ActionView::TestCase
     assert_equal '<p class="">limelight</p>', str
   end
 
+  def test_content_tag_with_conditional_hash_classes
+    str = content_tag("p", "limelight", class: { "song": true, "play": false })
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = content_tag("p", "limelight", class: [{ "song": true }, { "play": false }])
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = content_tag("p", "limelight", class: { song: true, play: false })
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = content_tag("p", "limelight", class: [{ song: true}, nil, false])
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = content_tag("p", "limelight", class: ["song", { foo: false}])
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = content_tag("p", "limelight", class: { "song": true, "play": true })
+    assert_equal "<p class=\"song play\">limelight</p>", str
+
+    str = content_tag("p", "limelight", class: { "song": false, "play": false })
+    assert_equal '<p class="">limelight</p>', str
+  end
+
+  def test_tag_builder_with_conditional_hash_classes
+    str = tag.p "limelight", class: { "song": true, "play": false }
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = tag.p "limelight", class: [{ "song": true }, { "play": false }]
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = tag.p "limelight", class: { song: true, play: false }
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = tag.p "limelight", class: [{ song: true}, nil, false]
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = tag.p "limelight", class: ["song", { foo: false}]
+    assert_equal "<p class=\"song\">limelight</p>", str
+
+    str = tag.p "limelight", class: { "song": true, "play": true }
+    assert_equal "<p class=\"song play\">limelight</p>", str
+
+    str = tag.p "limelight", class: { "song": false, "play": false }
+    assert_equal '<p class="">limelight</p>', str
+  end
+
+  def test_content_tag_with_unescaped_conditional_hash_classes
+    str = content_tag("p", "limelight", { class: { "song": true, "play>": true } }, false)
+    assert_equal "<p class=\"song play>\">limelight</p>", str
+
+    str = content_tag("p", "limelight", { class: ["song", { "play>": true }] }, false)
+    assert_equal "<p class=\"song play>\">limelight</p>", str
+  end
+
+  def test_tag_builder_with_unescaped_conditional_hash_classes
+    str = tag.p "limelight", class: { "song": true, "play>": true }, escape_attributes: false
+    assert_equal "<p class=\"song play>\">limelight</p>", str
+
+    str = tag.p "limelight", class: ["song", { "play>": true }], escape_attributes: false
+    assert_equal "<p class=\"song play>\">limelight</p>", str
+  end
+
   def test_content_tag_with_data_attributes
     assert_dom_equal '<p data-number="1" data-string="hello" data-string-with-quotes="double&quot;quote&quot;party&quot;">limelight</p>',
       content_tag("p", "limelight", data: { number: 1, string: "hello", string_with_quotes: 'double"quote"party"' })