diff --git a/app/src/main/java/org/communiquons/android/comunic/client/APIRequestTask.java b/app/src/main/java/org/communiquons/android/comunic/client/APIRequestTask.java
index c2cbf54..39d1b57 100644
--- a/app/src/main/java/org/communiquons/android/comunic/client/APIRequestTask.java
+++ b/app/src/main/java/org/communiquons/android/comunic/client/APIRequestTask.java
@@ -1,5 +1,8 @@
 package org.communiquons.android.comunic.client;
 
+import android.content.Context;
+import android.net.ConnectivityManager;
+import android.net.NetworkInfo;
 import android.os.AsyncTask;
 
 import org.json.JSONObject;
@@ -20,7 +23,6 @@ import java.net.URL;
  *
  * Created by pierre on 10/31/17.
  */
-//TODO Create APIResponse class
 abstract class APIRequestTask extends AsyncTask<APIRequestParameters, Void, APIResponse> {
 
     /**
@@ -83,11 +85,9 @@ abstract class APIRequestTask extends AsyncTask<APIRequestParameters, Void, APIR
 
 
             //Send request parameters
-            OutputStream out = conn.getOutputStream();
-            OutputStreamWriter outputStreamWriter = new OutputStreamWriter(out, "UTF-8");
-            BufferedWriter writer = new BufferedWriter(outputStreamWriter);
-            String parameters_encoded = parameters.get_parameters_encoded();
-            writer.write(parameters_encoded);
+            OutputStream out = new BufferedOutputStream(conn.getOutputStream());
+            BufferedWriter writer = new BufferedWriter (new OutputStreamWriter(out, "UTF-8"));
+            writer.write(parameters.get_parameters_encoded());
             writer.flush();
             writer.close();
             out.close();
@@ -95,7 +95,6 @@ abstract class APIRequestTask extends AsyncTask<APIRequestParameters, Void, APIR
             //Connect to the server
             conn.connect();
 
-
             //Get response code
             result.setResponse_code(conn.getResponseCode());
 
@@ -116,10 +115,24 @@ abstract class APIRequestTask extends AsyncTask<APIRequestParameters, Void, APIR
 
     // Reads an InputStream and converts it to a String.
     private String readIt(InputStream stream, int len) throws IOException {
-        Reader reader = null;
-        reader = new InputStreamReader(stream, "UTF-8");
+        Reader reader = new InputStreamReader(stream, "UTF-8");
         char[] buffer = new char[len];
         reader.read(buffer);
         return new String(buffer);
     }
+
+    /**
+     * Determine it is possible or not to connect to the API now
+     *
+     * @param context The context used to perform the test
+     * @return True if a network connection is available
+     */
+    static boolean isAPIavailable(Context context){
+        ConnectivityManager connMgr = (ConnectivityManager)
+                context.getSystemService(Context.CONNECTIVITY_SERVICE);
+
+        NetworkInfo networkInfo = connMgr.getActiveNetworkInfo();
+
+        return networkInfo != null && networkInfo.isConnected();
+    }
 }
diff --git a/app/src/main/java/org/communiquons/android/comunic/client/Account.java b/app/src/main/java/org/communiquons/android/comunic/client/Account.java
index e88cf91..dd3002f 100644
--- a/app/src/main/java/org/communiquons/android/comunic/client/Account.java
+++ b/app/src/main/java/org/communiquons/android/comunic/client/Account.java
@@ -110,7 +110,7 @@ class Account {
      * @param toks The array containing the tokens
      * @return False in case of failure
      */
-    private boolean save_new_tokens(ArrayList<String> toks){
+    boolean save_new_tokens(ArrayList<String> toks){
 
         //Create tokens array
         JSONArray tokens = new JSONArray();
diff --git a/app/src/main/java/org/communiquons/android/comunic/client/LoginActivity.java b/app/src/main/java/org/communiquons/android/comunic/client/LoginActivity.java
index 5a274e8..091afdf 100644
--- a/app/src/main/java/org/communiquons/android/comunic/client/LoginActivity.java
+++ b/app/src/main/java/org/communiquons/android/comunic/client/LoginActivity.java
@@ -1,16 +1,20 @@
 package org.communiquons.android.comunic.client;
 
+import android.content.Intent;
 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
-import android.util.Log;
 import android.view.View;
 import android.widget.EditText;
 import android.widget.ProgressBar;
 import android.widget.ScrollView;
+import android.widget.TextView;
 import android.widget.Toast;
 
+import org.json.JSONException;
 import org.json.JSONObject;
 
+import java.util.ArrayList;
+
 public class LoginActivity extends AppCompatActivity {
 
     /**
@@ -26,14 +30,17 @@ public class LoginActivity extends AppCompatActivity {
         //Create utilities object
         utils = new Utilities(this);
 
+        //Check for connectivity
+        if(!APIRequestTask.isAPIavailable(this)){
+            Toast.makeText(this, R.string.err_no_internet_connection, Toast.LENGTH_SHORT).show();
+        }
+
         //Make login submit button lives
         findViewById(R.id.login_submit).setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View v) {
-
                 //Submit login form
                 submitLogin();
-
             }
         });
 
@@ -46,7 +53,7 @@ public class LoginActivity extends AppCompatActivity {
     void submitLogin(){
 
         //Get the fields
-        EditText login_mail = (EditText) findViewById(R.id.email_field);
+        final EditText login_mail = (EditText) findViewById(R.id.email_field);
         EditText login_password = (EditText) findViewById(R.id.password_field);
 
 
@@ -66,11 +73,20 @@ public class LoginActivity extends AppCompatActivity {
             stop = 1;
         }
 
+        //Check internet connection
+        if(!APIRequestTask.isAPIavailable(this)){
+            show_form_error(getString(R.string.err_no_internet_connection));
+            stop = 1;
+        }
+
+
         //Stop if required
         if(stop != 0)
             return;
 
-        open_loading_state(true);
+        show_form_error("");
+        enter_loading_state(true);
+
 
         //Perform a request on the API to check user credentials and get login tokens
         APIRequestParameters params = new APIRequestParameters("user/connectUSER");
@@ -82,20 +98,73 @@ public class LoginActivity extends AppCompatActivity {
             @Override
             protected void onPostExecute(APIResponse result) {
 
-                open_loading_state(false);
+                //Check for errors
+                if(result == null) {
 
+                    //Hide loading wheel
+                    enter_loading_state(false);
 
+                    //Put the error on the login mail field
+                    show_form_error(getString(R.string.activity_login_err_invalid_credentials));
+                }
+
+                else
+                    //Perform next actions
+                    handle_server_response(result);
 
             }
         }.execute(params);
     }
 
+    /**
+     * Handle server responses that seems to accept a response
+     *
+     * @param response The server reponse
+     */
+    void handle_server_response(APIResponse response){
+
+        JSONObject data = response.getJSONObject();
+
+        //Check for decoding response errors
+        if(data == null) {
+            show_err_server_response();
+            return;
+        }
+
+        try {
+            //Search for tokens
+            JSONObject tokensObj = data.getJSONObject("tokens");
+
+            //Extract tokens
+            ArrayList<String> tokens = new ArrayList<>();
+            tokens.add(tokensObj.getString("token1"));
+            tokens.add(tokensObj.getString("token2"));
+
+            //Save tokens
+            Account account = new Account(this);
+            if(!account.save_new_tokens(tokens)) {
+                show_err_server_response();
+                return;
+            }
+
+        } catch (JSONException e){
+            e.printStackTrace();
+            show_err_server_response();
+            return;
+        }
+
+        //Redirect to the main activity
+        Intent redirect = new Intent(this, MainActivity.class);
+        startActivity(redirect);
+
+    }
+
     /**
      * Switch between loading state and ready state for the login form
      *
      * @param show_progress Specify wether a progress bar should be shown or not
      */
-    void open_loading_state(boolean show_progress){
+    void enter_loading_state(boolean show_progress){
         //Grab elements
         ProgressBar progressBar = (ProgressBar) findViewById(R.id.progress_bar);
         ScrollView login_form = (ScrollView) findViewById(R.id.login_form);
@@ -103,4 +172,33 @@ public class LoginActivity extends AppCompatActivity {
         progressBar.setVisibility(show_progress ? View.VISIBLE : View.GONE);
         login_form.setVisibility(show_progress ? View.GONE : View.VISIBLE);
     }
+
+    /**
+     * Display an error message on the login screen
+     *
+     * @param message The message to display on the screen
+     */
+    void show_form_error(String message){
+
+        //Retrieve error field
+        TextView v_error = (TextView) findViewById(R.id.login_error_message);
+
+        //Check what to do
+        boolean display = message.length() > 0;
+
+        //Make it visible (or hide it)
+        v_error.setVisibility(display ? View.VISIBLE : View.GONE);
+
+        //Set the text
+        v_error.setText(message);
+
+    }
+
+    /**
+     * Display an error message to say the server responded incorrectly to the request
+     */
+    void show_err_server_response(){
+        show_form_error(getString(R.string.activity_login_err_server_response));
+        enter_loading_state(false);
+    }
 }
diff --git a/app/src/main/java/org/communiquons/android/comunic/client/MainActivity.java b/app/src/main/java/org/communiquons/android/comunic/client/MainActivity.java
index 1ed3336..1eb8096 100644
--- a/app/src/main/java/org/communiquons/android/comunic/client/MainActivity.java
+++ b/app/src/main/java/org/communiquons/android/comunic/client/MainActivity.java
@@ -3,6 +3,7 @@ package org.communiquons.android.comunic.client;
 import android.content.Intent;
 import android.support.v7.app.AppCompatActivity;
 import android.os.Bundle;
+import android.widget.Toast;
 
 public class MainActivity extends AppCompatActivity {
 
@@ -16,6 +17,11 @@ public class MainActivity extends AppCompatActivity {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
 
+        //Check for connectivity
+        if(!APIRequestTask.isAPIavailable(this)){
+            Toast.makeText(this, R.string.err_no_internet_connection, Toast.LENGTH_SHORT).show();
+        }
+
         //Initialize account object
         account = new Account(this);
 
diff --git a/app/src/main/res/layout/activity_login.xml b/app/src/main/res/layout/activity_login.xml
index 0f2d98d..e14a9c9 100644
--- a/app/src/main/res/layout/activity_login.xml
+++ b/app/src/main/res/layout/activity_login.xml
@@ -31,6 +31,16 @@
             android:layout_height="wrap_content"
             android:orientation="vertical">
 
+            <!-- Error message -->
+            <TextView
+                android:id="@+id/login_error_message"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:textAlignment="center"
+                android:textColor="#FF2222"
+                tools:text="Error message"
+                android:visibility="gone"/>
+
             <!-- Email field -->
             <android.support.design.widget.TextInputLayout
                 android:layout_width="match_parent"
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index ac6fe86..79489dd 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -6,4 +6,7 @@
     <string name="activity_login_submit_form">Login</string>
     <string name="activity_login_err_invalid_password">The password is invalid!</string>
     <string name="activity_login_err_invalid_email">The email specified is invalid !</string>
+    <string name="activity_login_err_invalid_credentials">The connexion couldn\'t be etablished. Please check your credentials !</string>
+    <string name="err_no_internet_connection">No Internet connexion !</string>
+    <string name="activity_login_err_server_response">The server sent an unexcepted response…</string>
 </resources>