diff --git a/app/build.gradle b/app/build.gradle
index f12fb9a..fe54651 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -64,4 +64,16 @@ dependencies {
     // optional - Test helpers
     testImplementation "androidx.room:room-testing:$room_version"
     /*** Room Dependencies End ***/
+
+    /*** Retrofit Dependencies Start ***/
+    // 會連帶引用 OkHttp，因此不必再 implementation
+    // 這裡使用最新版，若要支援舊版 Android 請注意使用的版本。
+    // 詳見：https://github.com/square/retrofit/blob/master/CHANGELOG.md
+    implementation 'com.squareup.retrofit2:retrofit:2.9.0'
+    // 因為我們 API 格式為 JSON，因此使用 GSON 來幫忙轉為物件
+    implementation "com.squareup.retrofit2:converter-gson:2.9.0"
+    /*** Retrofit Dependencies End ***/
+
+    implementation "com.squareup.okhttp3:logging-interceptor:3.14.9"
+    testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.3.9'
 }
\ No newline at end of file
diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index 0dec640..7c687f4 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -2,6 +2,9 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="tw.andyang.kotlinandroidworkshop">
 
+    <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+
     <application
         android:allowBackup="true"
         android:icon="@mipmap/ic_launcher"
diff --git a/app/src/main/java/tw/andyang/kotlinandroidworkshop/TodoListFragment.kt b/app/src/main/java/tw/andyang/kotlinandroidworkshop/TodoListFragment.kt
index a6a429d..7e9e50e 100644
--- a/app/src/main/java/tw/andyang/kotlinandroidworkshop/TodoListFragment.kt
+++ b/app/src/main/java/tw/andyang/kotlinandroidworkshop/TodoListFragment.kt
@@ -1,18 +1,25 @@
 package tw.andyang.kotlinandroidworkshop
 
 import android.os.Bundle
+import android.util.Log
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
+import android.widget.Toast
 import androidx.fragment.app.Fragment
 import androidx.lifecycle.Observer
 import androidx.lifecycle.ViewModelProvider
 import androidx.navigation.fragment.findNavController
 import androidx.recyclerview.widget.DividerItemDecoration
 import androidx.recyclerview.widget.LinearLayoutManager
+import com.google.gson.Gson
 import kotlinx.android.synthetic.main.fragment_todo_list.*
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.GlobalScope
+import kotlinx.coroutines.launch
 import tw.andyang.kotlinandroidworkshop.database.AppDatabase
 import tw.andyang.kotlinandroidworkshop.mvvm.AnyViewModelFactory
+import tw.andyang.kotlinandroidworkshop.network.ApiClient
 import tw.andyang.kotlinandroidworkshop.repository.TodoItemRepository
 
 class TodoListFragment : Fragment() {
@@ -59,5 +66,16 @@ class TodoListFragment : Fragment() {
         buttonAdd.setOnClickListener {
             findNavController().navigate(TodoListFragmentDirections.actionMainFragmentToAddTodoFragment())
         }
+
+
+        GlobalScope.launch(Dispatchers.Main) {
+            val gson = Gson()
+            val client = ApiClient()
+            Log.d("Hello", gson.toJson(client.listUser()))
+            val userNames = client.listUser().map { it.lastName }
+            activity?.run {
+                Toast.makeText(this, userNames.joinToString(", "), Toast.LENGTH_LONG).show()
+            }
+        }
     }
 }
\ No newline at end of file
diff --git a/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/ApiClient.kt b/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/ApiClient.kt
new file mode 100644
index 0000000..369dc68
--- /dev/null
+++ b/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/ApiClient.kt
@@ -0,0 +1,69 @@
+package tw.andyang.kotlinandroidworkshop.network
+
+import okhttp3.Call
+import okhttp3.OkHttpClient
+import okhttp3.logging.HttpLoggingInterceptor
+import retrofit2.Retrofit
+import retrofit2.converter.gson.GsonConverterFactory
+import tw.andyang.kotlinandroidworkshop.network.entity.User
+
+class ApiClient {
+
+    private val okHttp: Call.Factory
+    private val retrofit: Retrofit
+    private val userApi: UserApi
+
+
+    constructor(baseUrl: String = "https://reqres.in/api/") {
+        this.okHttp = OkHttpClient.Builder()
+            .addInterceptor(HttpLoggingInterceptor().apply { setLevel(HttpLoggingInterceptor.Level.BODY); })
+            .build()
+        this.retrofit = Retrofit.Builder()
+            // 注意！base url 要斜線結尾！
+            .baseUrl(baseUrl)
+            .client(this.okHttp)
+            .addConverterFactory(GsonConverterFactory.create())
+            .build()
+
+        this.userApi = retrofit.create(UserApi::class.java)
+    }
+
+    suspend fun listUser(): List<User> {
+        try {
+            val response = userApi.listUser()
+            return if (response.isSuccessful) {
+                response.body()!!.data
+            } else {
+                throw Exception("should success")
+            }
+        } catch (e: Exception) {
+            throw e
+        }
+    }
+
+    suspend fun getUser(userId: Int): User {
+        try {
+            val response = userApi.getUser(userId)
+            return if (response.isSuccessful) {
+                response.body()!!.data
+            } else {
+                throw Exception("should success")
+            }
+        } catch (e: Exception) {
+            throw e
+        }
+    }
+
+    suspend fun createUser(userName: String, job: String): User {
+        try {
+            val response = userApi.createUser(userName, job)
+            return if (response.isSuccessful) {
+                response.body()!!
+            } else {
+                throw Exception("should success")
+            }
+        } catch (e: Exception) {
+            throw e
+        }
+    }
+}
\ No newline at end of file
diff --git a/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/UserApi.kt b/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/UserApi.kt
new file mode 100644
index 0000000..6f67142
--- /dev/null
+++ b/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/UserApi.kt
@@ -0,0 +1,24 @@
+package tw.andyang.kotlinandroidworkshop.network
+
+import retrofit2.Response
+import retrofit2.http.*
+import tw.andyang.kotlinandroidworkshop.network.entity.Envelope
+import tw.andyang.kotlinandroidworkshop.network.entity.User
+
+interface UserApi {
+
+    companion object {
+        const val PATH_ARG_USER_ID = "user_id"
+    }
+
+    // 注意！不要斜線開頭！
+    @GET("users")
+    suspend fun listUser(): Response<Envelope<List<User>>>
+
+    @GET("users/{$PATH_ARG_USER_ID}")
+    suspend fun getUser(@Path(PATH_ARG_USER_ID) userId: Int): Response<Envelope<User>>
+
+    @FormUrlEncoded
+    @POST("users")
+    suspend fun createUser(@Field("name") userName: String, @Field("job") job: String): Response<User>
+}
\ No newline at end of file
diff --git a/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/entity/Envelope.kt b/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/entity/Envelope.kt
new file mode 100644
index 0000000..62eadfb
--- /dev/null
+++ b/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/entity/Envelope.kt
@@ -0,0 +1,5 @@
+package tw.andyang.kotlinandroidworkshop.network.entity
+
+data class Envelope<T>(
+    val data: T
+)
\ No newline at end of file
diff --git a/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/entity/User.kt b/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/entity/User.kt
new file mode 100644
index 0000000..06580ff
--- /dev/null
+++ b/app/src/main/java/tw/andyang/kotlinandroidworkshop/network/entity/User.kt
@@ -0,0 +1,11 @@
+package tw.andyang.kotlinandroidworkshop.network.entity
+
+import com.google.gson.annotations.SerializedName
+
+class User(
+    @SerializedName("id") val id: Int,
+    @SerializedName("email") var email: String,
+    @SerializedName("first_name") var firstName: String,
+    @SerializedName("last_name") var lastName: String,
+    @SerializedName("avatar") var avatar: String
+)
\ No newline at end of file
diff --git a/app/src/main/java/tw/andyang/kotlinandroidworkshop/repository/UserRepository.kt b/app/src/main/java/tw/andyang/kotlinandroidworkshop/repository/UserRepository.kt
new file mode 100644
index 0000000..c785058
--- /dev/null
+++ b/app/src/main/java/tw/andyang/kotlinandroidworkshop/repository/UserRepository.kt
@@ -0,0 +1,15 @@
+package tw.andyang.kotlinandroidworkshop.repository
+
+import tw.andyang.kotlinandroidworkshop.network.ApiClient
+import tw.andyang.kotlinandroidworkshop.network.entity.User
+
+class UserRepository(private val apiClient: ApiClient) {
+
+    suspend fun listUser(): List<User> {
+        return apiClient.listUser()
+    }
+
+    suspend fun getUser(userId: Int): User {
+        return apiClient.getUser(userId)
+    }
+}
\ No newline at end of file
diff --git a/app/src/test/java/tw/andyang/kotlinandroidworkshop/network/ApiClientTest.kt b/app/src/test/java/tw/andyang/kotlinandroidworkshop/network/ApiClientTest.kt
new file mode 100644
index 0000000..b8dec06
--- /dev/null
+++ b/app/src/test/java/tw/andyang/kotlinandroidworkshop/network/ApiClientTest.kt
@@ -0,0 +1,62 @@
+package tw.andyang.kotlinandroidworkshop.network
+
+import com.google.gson.Gson
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.newSingleThreadContext
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.test.TestCoroutineDispatcher
+import kotlinx.coroutines.test.resetMain
+import kotlinx.coroutines.test.setMain
+import org.junit.After
+import org.junit.Before
+import org.junit.Test
+
+class ApiClientTest {
+
+    private val mainThreadSurrogate = newSingleThreadContext("UI thread")
+
+    @Before
+    fun setUp() {
+        Dispatchers.setMain(mainThreadSurrogate)
+    }
+
+    @After
+    fun tearDown() {
+        Dispatchers.resetMain() // reset main dispatcher to the original Main dispatcher
+        mainThreadSurrogate.close()
+    }
+
+    @Test
+    fun testListUser() {
+        runBlocking {
+            launch(Dispatchers.Main) {
+                val gson = Gson()
+                val apiClient = ApiClient()
+                println(gson.toJson(apiClient.listUser()))
+            }
+        }
+    }
+
+    @Test
+    fun testGetUser() {
+        runBlocking {
+            launch(Dispatchers.Main) {
+                val gson = Gson()
+                val apiClient = ApiClient()
+                println(gson.toJson(apiClient.getUser(1)))
+            }
+        }
+    }
+
+    @Test
+    fun testCreateUser() {
+        runBlocking {
+            launch(Dispatchers.Main) {
+                val gson = Gson()
+                val apiClient = ApiClient()
+                println(gson.toJson(apiClient.createUser("morpheus", "leader")))
+            }
+        }
+    }
+}
\ No newline at end of file