diff --git a/public/static/style.css b/public/static/style.css
index 6064a86..ba29d51 100644
--- a/public/static/style.css
+++ b/public/static/style.css
@@ -123,6 +123,11 @@ button {
     color: gray;
 }
 
+.margin_vertical_1rem {
+    margin-top: 1rem;
+    margin-bottom: 1rem;
+}
+
 /* -- Tables -- */
 
 table td, table th {
diff --git a/src/Common/FormData.php b/src/Common/FormData.php
index 24eaf68..2756aba 100644
--- a/src/Common/FormData.php
+++ b/src/Common/FormData.php
@@ -34,22 +34,27 @@ abstract class FormData
 
     // Input validation - Application specific validators
 
-    protected static function validateUsername(string $username, bool $required = true): ?string
+    protected static function validateUsername(string $username, bool $required = true, string $fieldName = 'Username'): ?string
     {
         if (!$required && $username === '') {
             return null;
         }
 
         $username = strtolower(
-            self::validateString($username, 3, 100, 'Username')
+            self::validateString($username, 3, 100, $fieldName)
         );
 
         if (!preg_match('/^[a-z0-9._+-]+@[a-z0-9.-]+$/', $username) || preg_match('/^\\.|\\.\\.|\\.@|@\\.|\\.$/', $username)) {
-            throw new InputValidationError('Username is not valid (must be a valid mail address).');
+            throw new InputValidationError("$fieldName is not valid (must be a valid mail address).");
         }
         return $username;
     }
 
+    protected static function validateAliasAddress(string $aliasAddress): string
+    {
+        return self::validateUsername($aliasAddress, true, 'Alias address');
+    }
+
     protected static function validatePassword(string $password, string $passwordRepeat, bool $required = true): ?string
     {
         if (!$required && $password === '' && $passwordRepeat === '') {
diff --git a/src/Frontend/Accounts/AccountAddAliasData.php b/src/Frontend/Accounts/AccountAddAliasData.php
new file mode 100644
index 0000000..306ca90
--- /dev/null
+++ b/src/Frontend/Accounts/AccountAddAliasData.php
@@ -0,0 +1,28 @@
+<?php
+declare(strict_types=1);
+
+namespace MailAccountAdmin\Frontend\Accounts;
+
+use MailAccountAdmin\Common\FormData;
+
+class AccountAddAliasData extends FormData
+{
+    private string $aliasAddress;
+
+    private function __construct(string $aliasAddress)
+    {
+        $this->aliasAddress = $aliasAddress;
+    }
+
+    public static function createFromArray($raw): self
+    {
+        return new self(
+            self::validateAliasAddress(trim($raw['alias_address'] ?? '')),
+        );
+    }
+
+    public function getAliasAddress(): string
+    {
+        return $this->aliasAddress;
+    }
+}
diff --git a/src/Frontend/Accounts/AccountController.php b/src/Frontend/Accounts/AccountController.php
index 4a6e268..1f9d6ac 100644
--- a/src/Frontend/Accounts/AccountController.php
+++ b/src/Frontend/Accounts/AccountController.php
@@ -64,6 +64,9 @@ class AccountController extends BaseController
             return $this->showAccount404($response, $accountId);
         }
 
+        // If the "add alias" form has been submitted, add the result message to the render data array
+        $renderData = $this->addLastActionResultToRenderData($renderData);
+
         return $this->view->render($response, 'account_details.html.twig', $renderData);
     }
 
@@ -210,4 +213,30 @@ class AccountController extends BaseController
         // Redirect to edit form page via GET (PRG)
         return $response->withHeader('Location', $redirectTarget)->withStatus(303);
     }
+
+
+    // -- /accounts/{id}/addalias - Create a new alias for the account
+
+    public function addAliasToAccount(Request $request, Response $response, array $args): Response
+    {
+        // Parse URL arguments and form data
+        $accountId = (int)$args['id'];
+        $addAliasData = $request->getParsedBody();
+
+        try {
+            // Validate input
+            $validatedAddAliasData = AccountAddAliasData::createFromArray($addAliasData);
+            $this->accountHandler->addAliasToAccount($accountId, $validatedAddAliasData);
+
+            // Save success result
+            $successMessage = "Alias <i>{$validatedAddAliasData->getAliasAddress()}</i> was added.";
+            $this->sessionHelper->setLastActionResult(ActionResult::createSuccessResult($successMessage));
+        } catch (InputValidationError $e) {
+            // Save error result
+            $this->sessionHelper->setLastActionResult(ActionResult::createErrorResult($e->getMessage(), $addAliasData));
+        }
+
+        // Redirect to edit form page via GET (PRG)
+        return $response->withHeader('Location', '/accounts/' . $accountId)->withStatus(303);
+    }
 }
diff --git a/src/Frontend/Accounts/AccountHandler.php b/src/Frontend/Accounts/AccountHandler.php
index 0556e6a..32dce32 100644
--- a/src/Frontend/Accounts/AccountHandler.php
+++ b/src/Frontend/Accounts/AccountHandler.php
@@ -265,4 +265,26 @@ class AccountHandler
             'deleted_alias_count' => $deleteAliasCount,
         ];
     }
+
+
+    // -- /accounts/{id}/addalias - Create a new alias for the account
+
+    public function addAliasToAccount(int $accountId, AccountAddAliasData $aliasAddData): void
+    {
+        // Check if account exists
+        try {
+            $this->accountRepository->fetchAccountById($accountId);
+        } catch (AccountNotFoundException $e) {
+            throw new InputValidationError('Account with ID ' . $accountId . ' does not exist!');
+        }
+
+        // Check if alias address is still available
+        $address = $aliasAddData->getAliasAddress();
+        if (!$this->accountRepository->checkUsernameAvailable($address) || !$this->aliasRepository->checkAliasAvailable($address)) {
+            throw new InputValidationError("Alias address \"$address\" is not available.");
+        }
+
+        // Create alias in database
+        $this->aliasRepository->createNewAlias($accountId, $address);
+    }
 }
diff --git a/src/Routes.php b/src/Routes.php
index 62faebd..00611ab 100644
--- a/src/Routes.php
+++ b/src/Routes.php
@@ -33,5 +33,6 @@ class Routes
         $app->post('/accounts/{id:[1-9][0-9]*}/edit', AccountController::class . ':editAccount');
         $app->get('/accounts/{id:[1-9][0-9]*}/delete', AccountController::class . ':showAccountDelete');
         $app->post('/accounts/{id:[1-9][0-9]*}/delete', AccountController::class . ':deleteAccount');
+        $app->post('/accounts/{id:[1-9][0-9]*}/addalias', AccountController::class . ':addAliasToAccount');
     }
 }
diff --git a/templates/account_details.html.twig b/templates/account_details.html.twig
index 5021452..4e00c14 100644
--- a/templates/account_details.html.twig
+++ b/templates/account_details.html.twig
@@ -82,4 +82,20 @@
     {% else %}
         <p>No aliases.</p>
     {% endif %}
+
+    <form action="/accounts/{{ id }}/addalias" method="POST">
+        {{ include('includes/form_result_box.html.twig') }}
+
+        <table class="margin_vertical_1rem">
+            <tr>
+                <td><label for="add_alias_address">New alias:</label></td>
+                <td><input id="add_alias_address" name="alias_address" value="{{ formData['new_alias'] | default('') }}"/></td>
+            </tr>
+            <tr>
+                <td colspan="2">
+                    <button type="submit">Add alias</button>
+                </td>
+            </tr>
+        </table>
+    </form>
 {% endblock %}