diff --git a/Gemfile b/Gemfile
index e3efa72..a6099ae 100644
--- a/Gemfile
+++ b/Gemfile
@@ -10,6 +10,7 @@ gem 'bootsnap', require: false
 gem 'draper'
 gem 'pg', '>= 0.18', '< 2.0'
 gem 'puma'
+gem 'pundit'
 gem 'rails', '= 5.2.2'
 gem 'slim-rails'
 gem 'webpacker', '~> 3' # 3.x does not support npm package webpack 4.x. Will be fixed in 4.x.
diff --git a/Gemfile.lock b/Gemfile.lock
index 8c961ee..814850c 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -124,6 +124,8 @@ GEM
     pry-rails (0.3.9)
       pry (>= 0.10.4)
     puma (3.12.0)
+    pundit (2.0.1)
+      activesupport (>= 3.0.0)
     rack (2.0.6)
     rack-proxy (0.6.5)
       rack
@@ -215,6 +217,7 @@ DEPENDENCIES
   pry-byebug
   pry-rails
   puma
+  pundit
   rails (= 5.2.2)
   slim-rails
   spring
diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index 7944f9f..ee5fd0e 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -1,4 +1,15 @@
 # frozen_string_literal: true
 
 class ApplicationController < ActionController::Base
+  include Pundit
+
+  delegate :current_user, to: :helpers, allow_nil: true
+
+  rescue_from Pundit::NotAuthorizedError, with: :redirect_user_back
+
+  private
+
+  def redirect_user_back
+    redirect_back(fallback_location: root_path, alert: 'You are not authorized to perform this action.')
+  end
 end
diff --git a/app/controllers/notes_controller.rb b/app/controllers/notes_controller.rb
index cd75764..76e1ea4 100644
--- a/app/controllers/notes_controller.rb
+++ b/app/controllers/notes_controller.rb
@@ -2,11 +2,12 @@
 
 class NotesController < ApplicationController
   def index
-    @notes = Note.not_ended.not_completed.decorate
+    @notes = policy_scope(Note).decorate
   end
 
   def show
     @note = Note.find(params[:id]).decorate
+    authorize(@note)
   end
 
   def new
@@ -25,10 +26,14 @@ def create
 
   def edit
     @note = Note.find(params[:id])
+    authorize(@note)
+
   end
 
   def update
     @note = Note.find(params[:id])
+    authorize(@note)
+
     if @note.update(note_params)
       redirect_to @note, notice: 'Note successfully updated.'
     else
@@ -38,18 +43,21 @@ def update
 
   def complete
     @note = Note.find(params[:id])
+    authorize(@note)
+
     service = Notes::Complete.new(note: @note)
     if service.save
       flash[:notice] = 'Note successfully marked as completed.'
+      redirect_to notes_path
     else
       flash[:alert] = "Note not marked as completed: #{service.errors.full_messages.join(', ')}"
+      redirect_to @note
     end
-    redirect_to @note
   end
 
   private
 
   def note_params
-    params.require(:note).permit(:title, :description, :started_at, :ended_at).merge(user: helpers.current_user)
+    params.require(:note).permit(:title, :description, :started_at, :ended_at).merge(user: current_user)
   end
 end
diff --git a/app/controllers/sessions_controller.rb b/app/controllers/sessions_controller.rb
index f376ce9..1af115b 100644
--- a/app/controllers/sessions_controller.rb
+++ b/app/controllers/sessions_controller.rb
@@ -2,10 +2,14 @@
 
 class SessionsController < ApplicationController
   def new
+    authorize(:session)
+
     @login = Login.new
   end
 
   def create
+    authorize(:session)
+
     @login = Login.new(user_params)
     if @login.save
       helpers.log_in(@login.user)
@@ -16,6 +20,8 @@ def create
   end
 
   def destroy
+    authorize(:session)
+
     helpers.log_out
     redirect_to notes_path, notice: 'Successfully logged out.'
   end
diff --git a/app/controllers/users_controller.rb b/app/controllers/users_controller.rb
index 6d90b0f..a5a64cc 100644
--- a/app/controllers/users_controller.rb
+++ b/app/controllers/users_controller.rb
@@ -2,10 +2,14 @@
 
 class UsersController < ApplicationController
   def new
+    authorize(:register)
+
     @register = Register.new
   end
 
   def create
+    authorize(:register)
+
     @register = Register.new(user_params)
     if @register.save
       helpers.log_in(@register.user)
diff --git a/app/policies/application_policy.rb b/app/policies/application_policy.rb
new file mode 100644
index 0000000..965fa3b
--- /dev/null
+++ b/app/policies/application_policy.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+class ApplicationPolicy
+  attr_reader :user, :record
+
+  class Scope
+    attr_reader :user, :scope
+
+    def initialize(user, scope)
+      @user = user
+      @scope = scope
+    end
+
+    def resolve
+      scope.all
+    end
+  end
+
+  def initialize(user, record)
+    @user = user
+    @record = record
+  end
+
+  def index?
+    false
+  end
+
+  def show?
+    false
+  end
+
+  def new?
+    create?
+  end
+
+  def create?
+    false
+  end
+
+  def edit?
+    update?
+  end
+
+  def update?
+    false
+  end
+
+  def destroy?
+    false
+  end
+
+  private
+
+  def logged_in?
+    user.present?
+  end
+end
diff --git a/app/policies/note_policy.rb b/app/policies/note_policy.rb
new file mode 100644
index 0000000..8b07f8c
--- /dev/null
+++ b/app/policies/note_policy.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+class NotePolicy < ApplicationPolicy
+  class Scope < Scope
+    def resolve
+      scope.not_completed.where(user: user.presence)
+    end
+  end
+
+  def show?
+    record.user == user.presence
+  end
+
+  def update?
+    return false if record.completed?
+
+    show?
+  end
+
+  def complete?
+    update?
+  end
+end
diff --git a/app/policies/register_policy.rb b/app/policies/register_policy.rb
new file mode 100644
index 0000000..48631d7
--- /dev/null
+++ b/app/policies/register_policy.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class RegisterPolicy < ApplicationPolicy
+  def create?
+    !logged_in?
+  end
+end
diff --git a/app/policies/session_policy.rb b/app/policies/session_policy.rb
new file mode 100644
index 0000000..78d67d2
--- /dev/null
+++ b/app/policies/session_policy.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class SessionPolicy < ApplicationPolicy
+  def create?
+    !logged_in?
+  end
+
+  def destroy?
+    logged_in?
+  end
+end