diff --git a/app/models/item_group.rb b/app/models/item_group.rb
new file mode 100644
index 00000000..5b1840dc
--- /dev/null
+++ b/app/models/item_group.rb
@@ -0,0 +1,6 @@
+class ItemGroup < ApplicationRecord
+  belongs_to :item, polymorphic: true
+  belongs_to :root_item, polymorphic: true
+
+  enum group_type: [:similar, :identical]
+end
diff --git a/app/models/user.rb b/app/models/user.rb
index 0848f17a..43176394 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -1,7 +1,7 @@
 class User < ApplicationRecord
-  belongs_to :group
+  belongs_to :user_group
 
-  delegate :study, to: :group
+  delegate :study, to: :user_group
 
   # Others available are:
   # :timeoutable and :omniauthable
diff --git a/app/models/user_group.rb b/app/models/user_group.rb
index e3d14127..7287e0b3 100644
--- a/app/models/user_group.rb
+++ b/app/models/user_group.rb
@@ -18,7 +18,7 @@ class UserGroup < ApplicationRecord
 
   private # Private methods
 
-  # In case more than just the study label is submitted extract the label for
+  # In case more than just the study label is submitted extract the label from
   # saving
   def remove_study_labelling
     if study.is_a? Array
diff --git a/db/migrate/20170517153047_create_item_groups.rb b/db/migrate/20170517153047_create_item_groups.rb
new file mode 100644
index 00000000..d2c518a8
--- /dev/null
+++ b/db/migrate/20170517153047_create_item_groups.rb
@@ -0,0 +1,11 @@
+class CreateItemGroups < ActiveRecord::Migration[5.0]
+  def change
+    create_table :item_groups do |t|
+      t.references :item, polymorphic: true
+      t.integer :group_type
+      t.references :root_item, polymorphic: true
+
+      t.timestamps
+    end
+  end
+end
diff --git a/db/structure.sql b/db/structure.sql
index ba660337..9288fde3 100644
--- a/db/structure.sql
+++ b/db/structure.sql
@@ -614,6 +614,41 @@ CREATE SEQUENCE instruments_id_seq
 ALTER SEQUENCE instruments_id_seq OWNED BY instruments.id;
 
 
+--
+-- Name: item_groups; Type: TABLE; Schema: public; Owner: -
+--
+
+CREATE TABLE item_groups (
+    id integer NOT NULL,
+    item_type character varying,
+    item_id integer,
+    group_type integer,
+    root_item_type character varying,
+    root_item_id integer,
+    created_at timestamp without time zone NOT NULL,
+    updated_at timestamp without time zone NOT NULL
+);
+
+
+--
+-- Name: item_groups_id_seq; Type: SEQUENCE; Schema: public; Owner: -
+--
+
+CREATE SEQUENCE item_groups_id_seq
+    START WITH 1
+    INCREMENT BY 1
+    NO MINVALUE
+    NO MAXVALUE
+    CACHE 1;
+
+
+--
+-- Name: item_groups_id_seq; Type: SEQUENCE OWNED BY; Schema: public; Owner: -
+--
+
+ALTER SEQUENCE item_groups_id_seq OWNED BY item_groups.id;
+
+
 --
 -- Name: links; Type: TABLE; Schema: public; Owner: -
 --
@@ -1221,6 +1256,13 @@ ALTER TABLE ONLY instruments ALTER COLUMN id SET DEFAULT nextval('instruments_id
 ALTER TABLE ONLY instruments_datasets ALTER COLUMN id SET DEFAULT nextval('instruments_datasets_id_seq'::regclass);
 
 
+--
+-- Name: id; Type: DEFAULT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY item_groups ALTER COLUMN id SET DEFAULT nextval('item_groups_id_seq'::regclass);
+
+
 --
 -- Name: id; Type: DEFAULT; Schema: public; Owner: -
 --
@@ -1495,6 +1537,14 @@ ALTER TABLE ONLY instruments
     ADD CONSTRAINT instruments_pkey PRIMARY KEY (id);
 
 
+--
+-- Name: item_groups_pkey; Type: CONSTRAINT; Schema: public; Owner: -
+--
+
+ALTER TABLE ONLY item_groups
+    ADD CONSTRAINT item_groups_pkey PRIMARY KEY (id);
+
+
 --
 -- Name: links_pkey; Type: CONSTRAINT; Schema: public; Owner: -
 --
@@ -1804,6 +1854,20 @@ CREATE INDEX index_instruments_datasets_on_dataset_id ON instruments_datasets US
 CREATE INDEX index_instruments_datasets_on_instrument_id ON instruments_datasets USING btree (instrument_id);
 
 
+--
+-- Name: index_item_groups_on_item_type_and_item_id; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE INDEX index_item_groups_on_item_type_and_item_id ON item_groups USING btree (item_type, item_id);
+
+
+--
+-- Name: index_item_groups_on_root_item_type_and_root_item_id; Type: INDEX; Schema: public; Owner: -
+--
+
+CREATE INDEX index_item_groups_on_root_item_type_and_root_item_id ON item_groups USING btree (root_item_type, root_item_id);
+
+
 --
 -- Name: index_links_on_target_type_and_target_id; Type: INDEX; Schema: public; Owner: -
 --
@@ -2332,6 +2396,7 @@ INSERT INTO schema_migrations (version) VALUES
 ('20170302132603'),
 ('20170302132849'),
 ('20170505135010'),
-('20170517105644');
+('20170517105644'),
+('20170517153047');
 
 
diff --git a/test/fixtures/item_groups.yml b/test/fixtures/item_groups.yml
new file mode 100644
index 00000000..ccf86aef
--- /dev/null
+++ b/test/fixtures/item_groups.yml
@@ -0,0 +1,15 @@
+# Read about fixtures at http://api.rubyonrails.org/classes/ActiveRecord/FixtureSet.html
+
+one:
+  item: one
+  item_type: Item
+  group_type: MyString
+  root_item: one
+  root_item_type: Root item
+
+two:
+  item: two
+  item_type: Item
+  group_type: MyString
+  root_item: two
+  root_item_type: Root item
diff --git a/test/models/item_group_test.rb b/test/models/item_group_test.rb
new file mode 100644
index 00000000..a6222987
--- /dev/null
+++ b/test/models/item_group_test.rb
@@ -0,0 +1,7 @@
+require 'test_helper'
+
+class ItemGroupTest < ActiveSupport::TestCase
+  # test "the truth" do
+  #   assert true
+  # end
+end