diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/README.md b/놀이터(예제 코드 작성)/solid-design-pattern-sample/README.md
index 2037f4e..7c410f4 100644
--- a/놀이터(예제 코드 작성)/solid-design-pattern-sample/README.md	
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/README.md	
@@ -115,6 +115,13 @@
 
 ### 옵저버(Observer) 패턴
 
+#### 구현 요구사항
+
+- 주문의 상태가 변경되면 배송팀과 운영팀에 알리고, 각각의 팀은 그에 따른 조치를 취한다.
+  - 배송팀은 배송을 시작한다.
+  - 운영팀은 고객에게 메시지를 전송한다.
+- 배송팀과 운영팀 외에 다른 팀에도 필요하다면 또 다른 팀에 메시지를 전송해야 할 수도 있다.
+
 ### 미디에이터(Mediator) 패턴
 
 ### 파사드(Facade) 패턴
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/DeliveryTeam.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/DeliveryTeam.kt
new file mode 100644
index 0000000..8212d2a
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/DeliveryTeam.kt	
@@ -0,0 +1,12 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.after
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+class DeliveryTeam : Team {
+    override val name: String
+        get() = "배송팀"
+
+    override fun onNotice(state: OrderState) {
+        println("$name : 주문이 ${state.description} 상태로 변경되었네요. 배송을 시작합니다.")
+    }
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/ManageTeam.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/ManageTeam.kt
new file mode 100644
index 0000000..66567f7
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/ManageTeam.kt	
@@ -0,0 +1,12 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.after
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+class ManageTeam : Team {
+    override val name: String
+        get() = "운영팀"
+
+    override fun onNotice(state: OrderState) {
+        println("$name : 주문이 ${state.description} 상태로 변경되었네요. 소비자에게 메시지를 전송합니다.")
+    }
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/Order.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/Order.kt
new file mode 100644
index 0000000..2f94bda
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/Order.kt	
@@ -0,0 +1,21 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.after
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+class Order(
+    private var state: OrderState = OrderState.RECEIVED,
+    private val teams: MutableList<Team> = mutableListOf()
+) {
+    fun addTeam(team: Team) {
+        this.teams.add(team)
+    }
+
+    fun removeTeam(team: Team) {
+        this.teams.remove(team)
+    }
+
+    fun changeState(state: OrderState) {
+        this.state = state
+        teams.forEach { it.onNotice(state) }
+    }
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/OrderApplication.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/OrderApplication.kt
new file mode 100644
index 0000000..d0cb1be
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/OrderApplication.kt	
@@ -0,0 +1,12 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.after
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+class OrderApplication
+
+fun main() {
+    val order = Order()
+    order.addTeam(DeliveryTeam())
+    order.addTeam(ManageTeam())
+    order.changeState(OrderState.DELIVERY_READY_COMPLETE)
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/Team.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/Team.kt
new file mode 100644
index 0000000..0cd62e0
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/after/Team.kt	
@@ -0,0 +1,9 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.after
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+interface Team {
+    val name: String
+
+    fun onNotice(state: OrderState)
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/DeliveryTeam.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/DeliveryTeam.kt
new file mode 100644
index 0000000..2a45e16
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/DeliveryTeam.kt	
@@ -0,0 +1,9 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.before
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+class DeliveryTeam {
+    fun doDelivery(state: OrderState) {
+        println("배송팀 : 주문이 ${state.description} 상태로 변경되었네요. 배송을 시작합니다.")
+    }
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/ManageTeam.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/ManageTeam.kt
new file mode 100644
index 0000000..3bd03c1
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/ManageTeam.kt	
@@ -0,0 +1,9 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.before
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+class ManageTeam {
+    fun sendMessage(state: OrderState) {
+        println("운영팀 : 주문이 ${state.description} 상태로 변경되었네요. 소비자에게 메시지를 전송합니다.")
+    }
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/Order.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/Order.kt
new file mode 100644
index 0000000..1596d73
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/Order.kt	
@@ -0,0 +1,15 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.before
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+class Order(
+    private var state: OrderState = OrderState.RECEIVED,
+    private val deliveryTeam: DeliveryTeam,
+    private val manageTeam: ManageTeam
+) {
+    fun changeState(state: OrderState) {
+        this.state = state
+        deliveryTeam.doDelivery(state)
+        manageTeam.sendMessage(state)
+    }
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/OrderApplication.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/OrderApplication.kt
new file mode 100644
index 0000000..7bf2021
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/before/OrderApplication.kt	
@@ -0,0 +1,10 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.before
+
+import com.banjjoknim.soliddesignpatternsample.designpattern.observer.common.OrderState
+
+class OrderApplication
+
+fun main() {
+    val order = Order(state = OrderState.RECEIVED, DeliveryTeam(), ManageTeam())
+    order.changeState(OrderState.DELIVERY_READY_COMPLETE)
+}
diff --git a/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/common/OrderState.kt b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/common/OrderState.kt
new file mode 100644
index 0000000..ab881ad
--- /dev/null
+++ b/놀이터(예제 코드 작성)/solid-design-pattern-sample/src/main/kotlin/com/banjjoknim/soliddesignpatternsample/designpattern/observer/common/OrderState.kt	
@@ -0,0 +1,8 @@
+package com.banjjoknim.soliddesignpatternsample.designpattern.observer.common
+
+enum class OrderState(
+    val description: String
+) {
+    RECEIVED("접수됨"),
+    DELIVERY_READY_COMPLETE("배송 준비")
+}