diff --git a/lib/pact_broker/pacts/content.rb b/lib/pact_broker/pacts/content.rb
index 05be78a95..5df54dfa3 100644
--- a/lib/pact_broker/pacts/content.rb
+++ b/lib/pact_broker/pacts/content.rb
@@ -1,9 +1,11 @@
 require 'pact_broker/pacts/parse'
 require 'pact_broker/pacts/sort_content'
+require 'pact_broker/pacts/generate_interaction_sha'
 
 module PactBroker
   module Pacts
     class Content
+      include GenerateInteractionSha
 
       def initialize pact_hash
         @pact_hash = pact_hash
@@ -29,6 +31,18 @@ def sort
         Content.from_hash(SortContent.call(pact_hash))
       end
 
+      def with_ids
+        new_pact_hash = pact_hash.dup
+        if interactions && interactions.is_a?(Array)
+          new_pact_hash['interactions'] = add_ids(interactions)
+        end
+
+        if messages && messages.is_a?(Array)
+          new_pact_hash['messages'] = add_ids(messages)
+        end
+        Content.from_hash(new_pact_hash)
+      end
+
       # Half thinking this belongs in GenerateSha
       def content_that_affects_verification_results
         if interactions || messages
@@ -61,6 +75,15 @@ def pact_specification_version
 
       attr_reader :pact_hash
 
+      def add_ids(interactions)
+        interactions.map do | interaction |
+          if interaction.is_a?(Hash)
+            interaction.merge("id" => generate_interaction_sha(interaction))
+          else
+            interaction
+          end
+        end
+      end
     end
   end
 end
diff --git a/lib/pact_broker/pacts/generate_interaction_sha.rb b/lib/pact_broker/pacts/generate_interaction_sha.rb
new file mode 100644
index 000000000..9be310bbf
--- /dev/null
+++ b/lib/pact_broker/pacts/generate_interaction_sha.rb
@@ -0,0 +1,23 @@
+require 'digest/sha1'
+require 'pact_broker/configuration'
+require 'pact_broker/pacts/sort_content'
+require 'pact_broker/pacts/parse'
+require 'pact_broker/pacts/content'
+
+module PactBroker
+  module Pacts
+    module GenerateInteractionSha
+      def self.call interaction_hash, options = {}
+        ordered_interaction_hash = interaction_hash.keys.sort.each_with_object({}) do | key, new_interaction_hash |
+          new_interaction_hash[key] = interaction_hash[key] unless key == "id"
+        end
+
+        Digest::SHA1.hexdigest(ordered_interaction_hash.to_json)
+      end
+
+      def generate_interaction_sha interaction_hash, options = {}
+        GenerateInteractionSha.call(interaction_hash, options)
+      end
+    end
+  end
+end
diff --git a/lib/pact_broker/pacts/service.rb b/lib/pact_broker/pacts/service.rb
index adf645c1f..9d935b417 100644
--- a/lib/pact_broker/pacts/service.rb
+++ b/lib/pact_broker/pacts/service.rb
@@ -121,7 +121,9 @@ def update_pact params, existing_pact
         logger.info "Updating existing pact publication with params #{params.reject{ |k, v| k == :json_content}}"
         logger.debug "Content #{params[:json_content]}"
         pact_version_sha = generate_sha(params[:json_content])
-        updated_pact = pact_repository.update(existing_pact.id, params.merge(pact_version_sha: pact_version_sha))
+        json_content = add_interaction_ids(params[:json_content])
+        update_params = { pact_version_sha: pact_version_sha, json_content: json_content }
+        updated_pact = pact_repository.update(existing_pact.id, update_params)
 
         webhook_service.trigger_webhooks updated_pact, nil, PactBroker::Webhooks::WebhookEvent::CONTRACT_PUBLISHED
         # TODO this should use the sha!
@@ -137,12 +139,15 @@ def update_pact params, existing_pact
       def create_pact params, version, provider
         logger.info "Creating new pact publication with params #{params.reject{ |k, v| k == :json_content}}"
         logger.debug "Content #{params[:json_content]}"
+        pact_version_sha = generate_sha(params[:json_content])
+        json_content = add_interaction_ids(params[:json_content])
         pact = pact_repository.create(
           json_content: params[:json_content],
           version_id: version.id,
           provider_id: provider.id,
           consumer_id: version.pacticipant_id,
-          pact_version_sha: generate_sha(params[:json_content])
+          pact_version_sha: pact_version_sha,
+          json_content: json_content
         )
         trigger_webhooks pact
         pact
@@ -152,6 +157,10 @@ def generate_sha(json_content)
         PactBroker.configuration.sha_generator.call(json_content)
       end
 
+      def add_interaction_ids(json_content)
+        Content.from_json(json_content).with_ids.to_json
+      end
+
       def trigger_webhooks pact
         # TODO add tests for this
         webhook_service.trigger_webhooks pact, nil, PactBroker::Webhooks::WebhookEvent::CONTRACT_PUBLISHED
diff --git a/spec/features/merge_pact_spec.rb b/spec/features/merge_pact_spec.rb
index 8b3f8264f..02aef8873 100644
--- a/spec/features/merge_pact_spec.rb
+++ b/spec/features/merge_pact_spec.rb
@@ -20,7 +20,7 @@
     end
 
     it "returns the pact in the body" do
-      expect(response_body_json).to include JSON.parse(pact_content)
+      expect(response_body_json).to match_pact JSON.parse(pact_content)
     end
   end
 
diff --git a/spec/features/publish_pact_spec.rb b/spec/features/publish_pact_spec.rb
index 71be0bb42..d8e381354 100644
--- a/spec/features/publish_pact_spec.rb
+++ b/spec/features/publish_pact_spec.rb
@@ -16,7 +16,7 @@
     end
 
     it "returns the pact in the body" do
-      expect(response_body_json).to include JSON.parse(pact_content)
+      expect(response_body_json).to match_pact JSON.parse(pact_content)
     end
   end
 
@@ -35,7 +35,7 @@
     end
 
     it "returns the pact in the response body" do
-      expect(response_body_json).to include JSON.parse(pact_content)
+      expect(response_body_json).to match_pact JSON.parse(pact_content)
     end
   end
 
diff --git a/spec/lib/pact_broker/pacts/content_spec.rb b/spec/lib/pact_broker/pacts/content_spec.rb
index 54c67f08e..8929b3ae8 100644
--- a/spec/lib/pact_broker/pacts/content_spec.rb
+++ b/spec/lib/pact_broker/pacts/content_spec.rb
@@ -3,6 +3,54 @@
 module PactBroker
   module Pacts
     describe Content do
+      describe "with_ids" do
+        let(:pact_hash) do
+          {
+            'ignored' => 'foo',
+            'interactions' => [interaction],
+            'metadata' => {
+              'foo' => 'bar'
+            }
+          }
+        end
+        let(:interaction) { { "foo" => "bar" } }
+
+        before do
+          allow(GenerateInteractionSha).to receive(:call).and_return("some-id")
+        end
+
+        context "when the interaction is a hash" do
+          it "adds ids to the interactions" do
+            expect(Content.from_hash(pact_hash).with_ids.interactions.first["id"]).to eq "some-id"
+          end
+        end
+
+        context "when the interaction is not a hash" do
+          let(:interaction) { 1 }
+
+          it "does not add an id" do
+            expect(Content.from_hash(pact_hash).with_ids.interactions.first).to eq interaction
+          end
+        end
+
+        context "when the pact is a message pact" do
+          let(:pact_hash) do
+            {
+              'ignored' => 'foo',
+              'messages' => [interaction],
+              'metadata' => {
+                'foo' => 'bar'
+              }
+            }
+          end
+
+          it "adds ids to the messages" do
+            expect(Content.from_hash(pact_hash).with_ids.messages.first["id"]).to eq "some-id"
+          end
+        end
+      end
+
+
       describe "content_that_affects_verification_results" do
 
         subject { Content.from_hash(pact_hash).content_that_affects_verification_results }
diff --git a/spec/lib/pact_broker/pacts/generate_interaction_sha_spec.rb b/spec/lib/pact_broker/pacts/generate_interaction_sha_spec.rb
new file mode 100644
index 000000000..37326e9f4
--- /dev/null
+++ b/spec/lib/pact_broker/pacts/generate_interaction_sha_spec.rb
@@ -0,0 +1,69 @@
+require 'pact_broker/pacts/generate_interaction_sha'
+
+module PactBroker
+  module Pacts
+    describe GenerateInteractionSha do
+      describe ".call" do
+        let(:interaction_hash) do
+          {
+            "description" => "foo",
+            "providerStates" => [
+              "name" => "bar",
+              "params" => {
+                "wiffle" => "bar",
+                "meep" => "eek"
+              }
+            ]
+          }
+        end
+
+        let(:interaction_hash_with_different_key_order) do
+          {
+            "providerStates" => [
+              "name" => "bar",
+              "params" => {
+                "wiffle" => "bar",
+                "meep" => "eek"
+              }
+            ],
+            "description" => "foo"
+          }
+        end
+
+        let(:interaction_hash_with_different_params_order) do
+          {
+            "description" => "foo",
+            "providerStates" => [
+              "name" => "bar",
+              "params" => {
+                "meep" => "eek",
+                "wiffle" => "bar"
+              }
+            ]
+          }
+        end
+
+        it "generates a SHA based on the sorted keys" do
+          expect(GenerateInteractionSha.call(interaction_hash)).to eq "5ec1cc12132d3437a5a2ced5537cdab2d4f44521"
+        end
+
+        it "generates the same SHA if the top level keys are ordered differently" do
+          expect(GenerateInteractionSha.call(interaction_hash)).to eq GenerateInteractionSha.call(interaction_hash_with_different_key_order)
+        end
+
+        # This could be a whole lot smarter, but I'm not sure it's worth it.
+        # eg. order of provider state params doesn't matter, but the ordering
+        # of the provider states themselves may... who knows.
+        # Let's not try and be too smart about it until we have a use case to flesh it out.
+        it "generates a different SHA if any of the other keys are ordered differently" do
+          expect(GenerateInteractionSha.call(interaction_hash)).to_not eq GenerateInteractionSha.call(interaction_hash_with_different_params_order)
+        end
+
+        it "ignores any existing id in the hash" do
+          interaction_hash["id"] = "foo"
+          expect(GenerateInteractionSha.call(interaction_hash)).to eq "5ec1cc12132d3437a5a2ced5537cdab2d4f44521"
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/pact_broker/pacts/service_spec.rb b/spec/lib/pact_broker/pacts/service_spec.rb
index e4f4fd2bb..87e92e278 100644
--- a/spec/lib/pact_broker/pacts/service_spec.rb
+++ b/spec/lib/pact_broker/pacts/service_spec.rb
@@ -31,6 +31,7 @@ module Pacts
         let(:existing_pact) { nil }
         let(:new_pact) { double('new_pact', json_content: json_content) }
         let(:json_content) { { the: "contract" }.to_json }
+        let(:json_content_with_ids) { { the: "contract with ids" }.to_json }
         let(:previous_pacts) { [] }
         let(:params) do
           {
@@ -40,10 +41,30 @@ module Pacts
             json_content: json_content
           }
         end
+        let(:content) { double('content') }
+        let(:content_with_interaction_ids) { double('content_with_interaction_ids', to_json: json_content_with_ids) }
+
+        before do
+          allow(Content).to receive(:from_json).and_return(content)
+          allow(content).to receive(:with_ids).and_return(content_with_interaction_ids)
+          allow(PactBroker::Pacts::GenerateSha).to receive(:call).and_call_original
+        end
 
         subject { Service.create_or_update_pact(params) }
 
+
         context "when no pact exists with the same params" do
+          it "creates the sha before adding the interaction ids" do
+            expect(PactBroker::Pacts::GenerateSha).to receive(:call).ordered
+            expect(content).to receive(:with_ids).ordered
+            subject
+          end
+
+          it "saves the pact interactions/messages with ids added to them" do
+            expect(pact_repository).to receive(:create).with hash_including(json_content: json_content_with_ids)
+            subject
+          end
+
           it "triggers webhooks for contract publications" do
             expect(webhook_service).to receive(:trigger_webhooks).with(new_pact, nil, PactBroker::Webhooks::WebhookEvent::CONTRACT_PUBLISHED)
             subject
@@ -53,6 +74,17 @@ module Pacts
         context "when a pact exists with the same params" do
           let(:existing_pact) { double('existing_pact', id: 4, json_content: { the: "contract" }.to_json) }
 
+          it "creates the sha before adding the interaction ids" do
+            expect(PactBroker::Pacts::GenerateSha).to receive(:call).ordered
+            expect(content).to receive(:with_ids).ordered
+            subject
+          end
+
+          it "saves the pact interactions/messages with ids added to them" do
+            expect(pact_repository).to receive(:update).with(anything, hash_including(json_content: json_content_with_ids))
+            subject
+          end
+
           it "triggers webhooks for contract publications" do
             expect(webhook_service).to receive(:trigger_webhooks).with(new_pact, nil, PactBroker::Webhooks::WebhookEvent::CONTRACT_PUBLISHED)
             subject