diff --git a/core/shared/src/main/scala/works/iterative/entity/AggregateError.scala b/core/shared/src/main/scala/works/iterative/entity/AggregateError.scala
new file mode 100644
index 0000000..9b8f18c
--- /dev/null
+++ b/core/shared/src/main/scala/works/iterative/entity/AggregateError.scala
@@ -0,0 +1,6 @@
+package works.iterative.entity
+
+import works.iterative.core.UserMessage
+
+trait AggregateError:
+  def userMessage: UserMessage

diff --git a/core/shared/src/main/scala/works/iterative/entity/AggregateError.scala b/core/shared/src/main/scala/works/iterative/entity/AggregateError.scala
new file mode 100644
index 0000000..9b8f18c
--- /dev/null
+++ b/core/shared/src/main/scala/works/iterative/entity/AggregateError.scala
@@ -0,0 +1,6 @@
+package works.iterative.entity
+
+import works.iterative.core.UserMessage
+
+trait AggregateError:
+  def userMessage: UserMessage
diff --git a/core/shared/src/main/scala/works/iterative/entity/AggregateRoot.scala b/core/shared/src/main/scala/works/iterative/entity/AggregateRoot.scala
new file mode 100644
index 0000000..2bc42b4
--- /dev/null
+++ b/core/shared/src/main/scala/works/iterative/entity/AggregateRoot.scala
@@ -0,0 +1,23 @@
+package works.iterative.entity
+
+import zio.*
+
+/** Represents aggregate root in DDD
+  *
+  * @tparam Id
+  *   Aggregate root id
+  * @tparam Command
+  *   Aggregate root command
+  * @tparam Event
+  *   Aggregate root event
+  * @tparam State
+  *   Aggregate root state
+  */
+trait AggregateRoot[Id, Command, Event, State, Error <: AggregateError]:
+  /** Aggregate root id */
+  def id: Id
+
+  /** Current state */
+  def state: UIO[State]
+
+  def handle(command: Command): IO[Error, Unit]