diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4572b9f7..2f5e7d87 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 3.1.0 (Unreleased)
+## 4.0.0 (Unreleased)
 
 ##### Breaking change: if you use a custom initializer for PaperTrail in conjunction with Rails, you will need to add this line of code to the beginning of it:
 ```ruby
@@ -38,7 +38,7 @@ PaperTrail::Rails::Engine.eager_load!
 
   - [#401](https://github.com/airblade/paper_trail/issues/401) / [#406](https://github.com/airblade/paper_trail/issues/406)
     `PaperTrail::Version` class is not loaded via a `Rails::Engine`, even when the gem is used with in Rails. This feature has
-    will be re-introduced in version `3.1.0`.
+    will be re-introduced in version `4.0`.
   - [#398](https://github.com/airblade/paper_trail/pull/398) - Only require the `RSpec` helper if `RSpec::Core` is required.
 
 ## 3.0.3
@@ -94,8 +94,8 @@ in the `PaperTrail::Version` class through a `Rails::Engine` when the gem is use
   - [#312](https://github.com/airblade/paper_trail/issues/312) - Fix RSpec `with_versioning` class level helper method.
   - `model_instance.without_versioning` now yields the `model_instance`, enabling syntax like this:
     `model_instance.without_versioning { |obj| obj.update_attributes(:name => 'value') }`.
-  - Deprecated `Model.paper_trail_on` and `Model.paper_trail_off` in favor of bang versions of the methods. Deprecation warning
-    informs users that the non-bang versions of the methods will be removed in version `3.1.0`.
+  - Deprecated `Model.paper_trail_on` and `Model.paper_trail_off` in favor of bang versions of the methods.
+    Deprecation warning informs users that the non-bang versions of the methods will be removed in version `4.0`
 
 ## 3.0.0
 
diff --git a/README.md b/README.md
index 586b0834..dd93ec5e 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@ There's an excellent [RailsCast on implementing Undo with Paper Trail](http://ra
 
 ## Compatibility
 
-Works with ActiveRecord 4 and ActiveRecord 3. Note: this code is on the `master` branch and tagged `v3.x`.
+Works with `ActiveRecord` 3+. Note: this code is on the `master` branch and tagged `v4.x`.
 
 Version 2 is on the branch named [`2.7-stable`](https://github.com/airblade/paper_trail/tree/2.7-stable) and is tagged `v2.x`, and works with Rails 3.
 
@@ -495,7 +495,7 @@ You can avoid having to do this manually by setting your initializer to pick up
 ```ruby
 # config/initializers/paper_trail.rb
 
-# the following line is required for PaperTrail >= 3.1.0 with Rails
+# the following line is required for PaperTrail >= 4.0.0 with Rails
 PaperTrail::Rails::Engine.eager_load!
 
 if defined?(::Rails::Console)
@@ -575,7 +575,7 @@ If you only use custom version classes and don't use PaperTrail's built-in one,
 ```ruby
 # config/initializers/paper_trail.rb
 
-# the following line is required for PaperTrail >= 3.1.0 with Rails
+# the following line is required for PaperTrail >= 4.0.0 with Rails
 PaperTrail::Rails::Engine.eager_load!
 
 PaperTrail::Version.module_eval do
@@ -771,7 +771,7 @@ For example:
 ```ruby
 # config/initializers/paper_trail.rb
 
-# the following line is required for PaperTrail >= 3.1.0 with Rails
+# the following line is required for PaperTrail >= 4.0.0 with Rails
 PaperTrail::Rails::Engine.eager_load!
 
 module PaperTrail
diff --git a/lib/paper_trail/has_paper_trail.rb b/lib/paper_trail/has_paper_trail.rb
index 1760c9b9..6b414564 100644
--- a/lib/paper_trail/has_paper_trail.rb
+++ b/lib/paper_trail/has_paper_trail.rb
@@ -91,7 +91,7 @@ module PaperTrail
       end
 
       def paper_trail_off
-        warn "DEPRECATED: use `paper_trail_off!` instead of `paper_trail_off`. Support for `paper_trail_off` will be removed in PaperTrail 3.1"
+        warn "DEPRECATED: use `paper_trail_off!` instead of `paper_trail_off`. Support for `paper_trail_off` will be removed in PaperTrail 4.0"
         self.paper_trail_off!
       end
 
@@ -101,7 +101,7 @@ module PaperTrail
       end
 
       def paper_trail_on
-        warn "DEPRECATED: use `paper_trail_on!` instead of `paper_trail_on`. Support for `paper_trail_on` will be removed in PaperTrail 3.1"
+        warn "DEPRECATED: use `paper_trail_on!` instead of `paper_trail_on`. Support for `paper_trail_on` will be removed in PaperTrail 4.0"
         self.paper_trail_on!
       end
 
diff --git a/lib/paper_trail/version_number.rb b/lib/paper_trail/version_number.rb
index 983c4659..fd7405fd 100644
--- a/lib/paper_trail/version_number.rb
+++ b/lib/paper_trail/version_number.rb
@@ -1,7 +1,7 @@
 module PaperTrail
   module VERSION
-    MAJOR = 3
-    MINOR = 1
+    MAJOR = 4
+    MINOR = 0
     TINY  = 0
     PRE   = 'alpha'
 
diff --git a/spec/models/widget_spec.rb b/spec/models/widget_spec.rb
index a1ff9aab..d621fd3a 100644
--- a/spec/models/widget_spec.rb
+++ b/spec/models/widget_spec.rb
@@ -274,7 +274,7 @@ describe Widget, :type => :model do
         end
 
         it 'should display a deprecation warning' do
-          is_expected.to receive(:warn).with("DEPRECATED: use `paper_trail_on!` instead of `paper_trail_on`. Support for `paper_trail_on` will be removed in PaperTrail 3.1")
+          is_expected.to receive(:warn).with("DEPRECATED: use `paper_trail_on!` instead of `paper_trail_on`. Support for `paper_trail_on` will be removed in PaperTrail 4.0")
           subject.paper_trail_on
         end
       end
@@ -303,7 +303,7 @@ describe Widget, :type => :model do
         end
 
         it 'should display a deprecation warning' do
-          is_expected.to receive(:warn).with("DEPRECATED: use `paper_trail_on!` instead of `paper_trail_on`. Support for `paper_trail_on` will be removed in PaperTrail 3.1")
+          is_expected.to receive(:warn).with("DEPRECATED: use `paper_trail_on!` instead of `paper_trail_on`. Support for `paper_trail_on` will be removed in PaperTrail 4.0")
           subject.paper_trail_on
         end
       end