diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1b16ced..91d2b3c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,11 +1,16 @@
 ## [Unreleased]
 ### Breaking Changes
 - Set a default primary key of `:id` to all models
+- All models require a primary key attribute to be present on each created entity
+- All entities are now deduplicated on their primary key value - but only when `caching` is enabled on the model
 
 ### Removed
 
 ### Added
 - Add ability to change the default primary key for all models by using `TestingRecord.default_primary_key = :my_id`
+- Added ability to filter model on `primary_key` attribute
+  - `.with_primary_key?` -> An entity exists with the `primary_key` value specified
+  - `.with_primary_key` -> Returns the entity with the `primary_key` value specified
 
 ### Changed
 - Deletion calls will now also purge `.current` if the deleted entity is the current entity when caching is enabled
@@ -40,7 +45,7 @@ add all helpers to all attributes on a model
 ## [0.6] - 2026-02-09
 ### Added
 - Added ability to filter model on `id` attribute
-  - `.with_id?` -> An entity exists that with the id specified
+  - `.with_id?` -> An entity exists with the id specified
   - `.with_id` -> Returns the entity with the id specified
 - Added ability to delete models where caching is enabled
 - When updating models, the cache is also updated to reflect the new values
diff --git a/lib/testing_record/dsl/builder/filters.rb b/lib/testing_record/dsl/builder/filters.rb
index e29272c..9f57cfc 100644
--- a/lib/testing_record/dsl/builder/filters.rb
+++ b/lib/testing_record/dsl/builder/filters.rb
@@ -36,6 +36,21 @@ def with_id(id)
           find_by({ id: })&.first&.tap { |entity| entity.class.current = entity }
         end
 
+        # Checks to see whether an entity exists with the provided primary_key
+        #
+        # @return [Boolean]
+        def with_primary_key?(primary_key)
+          !with_primary_key(primary_key).nil?
+        end
+
+        # Finds an entity with the provided primary_key
+        #   If one is found, set it as the current entity
+        #
+        # @return [TestingRecord::Model, nil]
+        def with_primary_key(primary_key)
+          find_by({ __primary_key => primary_key })&.first&.tap { |entity| entity.class.current = entity }
+        end
+
         private
 
         # Finds all entities that match specified attribute values
diff --git a/lib/testing_record/error.rb b/lib/testing_record/error.rb
index f9ab861..349cdf8 100644
--- a/lib/testing_record/error.rb
+++ b/lib/testing_record/error.rb
@@ -2,6 +2,8 @@
 
 module TestingRecord
   module Error
+    class AttributeError < StandardError; end
+    class EntityError < StandardError; end
     class InvalidConfigurationError < StandardError; end
   end
 end
diff --git a/lib/testing_record/model.rb b/lib/testing_record/model.rb
index 22f3122..9cff562 100644
--- a/lib/testing_record/model.rb
+++ b/lib/testing_record/model.rb
@@ -17,19 +17,24 @@ class << self
       attr_reader :current
 
       # Creates an instance of the model
-      #   -> Creating iVar values for each attribute that was provided
-      #   -> Adding it to the cache if caching is enabled
-      #   -> Keeping a track of all originally supplied attributes in symbolized format in the `attributes` iVar
+      #   -> Ensures that the primary key is specified in the attribute payload
+      #   -> Validates that a duplicate entity has not been made (If caching is enabled)
+      #   -> Creates iVar values (Symbol format) and attr_reader's for each attribute that was provided
+      #   -> Adds helper methods (If the model has been configured to include helpers)
+      #   -> Adds it to the cache (If caching is enabled)
       #
       # @return [TestingRecord::Model]
       def create(attributes)
-        new(attributes.transform_keys(&:to_sym)).tap do |entity|
-          configure_data(entity, attributes)
-          add_helpers(attributes) if entity.class.instance_variable_get(:@include_helpers)
-          cache_entity(entity)
+        if respond_to?(:all)
+          create_with_caching(attributes)
+        else
+          create_without_caching(attributes)
         end
       end
 
+      # Sets the current entity instance to the one supplied (Or removes it if supplied `nil`)
+      #
+      # @return [TestingRecord::Model, nil]
       def current=(entity)
         if entity
           TestingRecord.logger.info("Switching current user from #{@current} to #{entity}")
@@ -58,9 +63,25 @@ def delete_by_id(id)
 
       private
 
-      def cache_entity(entity)
-        return unless respond_to?(:all)
+      def create_with_caching(attributes)
+        ensure_primary_key_presence(attributes)
+        ensure_deduplication(attributes)
+        new(attributes.transform_keys(&:to_sym)).tap do |entity|
+          configure_data(entity, attributes)
+          add_helpers(attributes) if entity.class.instance_variable_get(:@include_helpers)
+          cache_entity(entity)
+        end
+      end
+
+      def create_without_caching(attributes)
+        ensure_primary_key_presence(attributes)
+        new(attributes.transform_keys(&:to_sym)).tap do |entity|
+          configure_data(entity, attributes)
+          add_helpers(attributes) if entity.class.instance_variable_get(:@include_helpers)
+        end
+      end
 
+      def cache_entity(entity)
         self.current = entity
         all << entity
         TestingRecord.logger.debug("Entity: #{entity} added to cache")
@@ -72,6 +93,20 @@ def configure_data(entity, attributes)
           entity.class.attr_reader attribute_key
         end
       end
+
+      def ensure_deduplication(attributes)
+        pk_value = attributes[__primary_key]
+        return unless with_primary_key?(pk_value)
+
+        TestingRecord.logger.error("#{name} entity already exists with primary key: #{pk_value}")
+        raise Error::EntityError, "#{name} entity already exists with primary key: #{pk_value}"
+      end
+
+      def ensure_primary_key_presence(attributes)
+        return if attributes.key?(__primary_key)
+
+        raise Error::AttributeError, "#{name} entity has not been supplied with the primary key: #{__primary_key}"
+      end
     end
 
     def initialize(attributes = {})
diff --git a/spec/testing_record/dsl/builder/filters_spec.rb b/spec/testing_record/dsl/builder/filters_spec.rb
index 2abf7ca..2ae97e8 100644
--- a/spec/testing_record/dsl/builder/filters_spec.rb
+++ b/spec/testing_record/dsl/builder/filters_spec.rb
@@ -4,6 +4,7 @@
   subject(:model_klazz) do
     Class.new(TestingRecord::Model) do
       caching :enabled
+      primary_key :email_address
     end
   end
 
@@ -48,6 +49,9 @@
   end
 
   describe '.with_id' do
+    before { model_klazz.primary_key :id }
+    after { model_klazz.primary_key :email_address }
+
     context 'when entity does not exist' do
       it 'does not find a model' do
         expect(model_klazz.with_id(1)).to be_nil
@@ -67,6 +71,9 @@
   end
 
   describe '.with_id?' do
+    before { model_klazz.primary_key :id }
+    after { model_klazz.primary_key :email_address }
+
     context 'when entity does not exist' do
       it 'is `false`' do
         expect(model_klazz.with_id?(1)).to be false
@@ -84,4 +91,48 @@
       end
     end
   end
+
+  describe '.with_primary_key' do
+    before { model_klazz.primary_key :peekay }
+    after { model_klazz.primary_key :email_address }
+
+    context 'when entity does not exist' do
+      it 'does not find a model' do
+        expect(model_klazz.with_primary_key(1)).to be_nil
+      end
+    end
+
+    context 'when entity exists' do
+      before do
+        model_klazz.create({ peekay: 1 })
+        model_klazz.create({ peekay: 2 })
+      end
+
+      it 'finds the first matching model' do
+        expect(model_klazz.with_primary_key(1)).to be_a TestingRecord::Model
+      end
+    end
+  end
+
+  describe '.with_primary_key?' do
+    before { model_klazz.primary_key :peekay }
+    after { model_klazz.primary_key :email_address }
+
+    context 'when entity does not exist' do
+      it 'is `false`' do
+        expect(model_klazz.with_primary_key?(1)).to be false
+      end
+    end
+
+    context 'when entity exists' do
+      before do
+        model_klazz.create({ peekay: 1 })
+        model_klazz.create({ peekay: 2 })
+      end
+
+      it 'is `true`' do
+        expect(model_klazz.with_primary_key?(1)).to be true
+      end
+    end
+  end
 end
diff --git a/spec/testing_record/dsl/builder/helpers_spec.rb b/spec/testing_record/dsl/builder/helpers_spec.rb
index 58a9a06..035e353 100644
--- a/spec/testing_record/dsl/builder/helpers_spec.rb
+++ b/spec/testing_record/dsl/builder/helpers_spec.rb
@@ -4,6 +4,7 @@
   subject(:klazz) do
     Class.new(TestingRecord::Model) do
       include_helpers
+      primary_key :foo
     end
   end
 
diff --git a/spec/testing_record/model_spec.rb b/spec/testing_record/model_spec.rb
index 7bad61c..90737be 100644
--- a/spec/testing_record/model_spec.rb
+++ b/spec/testing_record/model_spec.rb
@@ -1,8 +1,9 @@
 # frozen_string_literal: true
 
 RSpec.describe TestingRecord::Model do
-  let(:primary_model_entity) { FakeModel.create({ id: 1, foo: :foo, bar: :bar }) }
-  let(:secondary_model_entity) { FakeOtherModel.create({ id: 1, foo: :foo, bar: :bar }) }
+  let(:primary_model_entity) { FakeModel.create(model_attributes) }
+  let(:model_attributes) { { id: 1, foo: :foo, bar: :bar } }
+  let(:secondary_model_entity) { FakeOtherModel.create(model_attributes) }
 
   before do
     silence_logger!
@@ -14,10 +15,38 @@
     context 'with caching enabled' do
       before { FakeModel.caching :enabled }
 
+      it 'ensures that the primary key attribute was set in the attributes hash' do
+        expect(FakeModel).to receive(:ensure_primary_key_presence).with(model_attributes)
+
+        primary_model_entity
+      end
+
+      it 'does not permit an entity to be created without a primary key' do
+        expect { FakeModel.create({ foo: :no_primary_key }) }
+          .to raise_error(TestingRecord::Error::AttributeError)
+          .with_message('FakeModel entity has not been supplied with the primary key: id')
+      end
+
+      it 'does not permit an entity to be created with the same primary key' do
+        primary_model_entity
+
+        expect { FakeModel.create({ id: 1, other_key: :whatever }) }
+          .to raise_error(TestingRecord::Error::EntityError)
+          .with_message('FakeModel entity already exists with primary key: 1')
+      end
+
       it 'generates a new instance of the entity' do
         expect(primary_model_entity).to be_a FakeModel
       end
 
+      it 'creates a model with all the supplied attributes as iVars' do
+        expect(primary_model_entity.instance_variables).to contain_exactly(:@attributes, :@id, :@foo, :@bar)
+      end
+
+      it 'creates a model with all the supplied attributes as attr_readers' do
+        expect(primary_model_entity).to respond_to(:attributes, :id, :foo, :bar)
+      end
+
       it 'adds the entity to the cache' do
         expect { primary_model_entity }.to change(FakeModel.all, :length).by(1)
       end
@@ -32,9 +61,29 @@
     context 'without caching enabled' do
       before { FakeModel.caching :disabled }
 
+      it 'ensures that the primary key attribute was set in the attributes hash' do
+        expect(FakeModel).to receive(:ensure_primary_key_presence).with(model_attributes)
+
+        primary_model_entity
+      end
+
+      it 'does not permit an entity to be created without a primary key' do
+        expect { FakeModel.create({ foo: :no_primary_key }) }
+          .to raise_error(TestingRecord::Error::AttributeError)
+          .with_message('FakeModel entity has not been supplied with the primary key: id')
+      end
+
       it 'generates a new instance of the entity' do
         expect(primary_model_entity).to be_a FakeModel
       end
+
+      it 'creates a model with all the supplied attributes as iVars' do
+        expect(primary_model_entity.instance_variables).to contain_exactly(:@attributes, :@id, :@foo, :@bar)
+      end
+
+      it 'creates a model with all the supplied attributes as attr_readers' do
+        expect(primary_model_entity).to respond_to(:attributes, :id, :foo, :bar)
+      end
     end
   end