diff --git a/app/models/group.rb b/app/models/group.rb
new file mode 100644
--- /dev/null
+++ b/app/models/group.rb
@@ -0,0 +1,5 @@
+class Group < ActiveRecord::Base
+  has_and_belongs_to_many :problems
+  has_and_belongs_to_many :users
+end
+