<html>
<body>
<form action="form-action.php">
<select name="cars" multiple>
<option value="volvo">Volvo</option>
<option value="saab">Saab</option>
<option value="opel">Opel</option>
<option value="audi">Audi</option>
</select>
<input type="submit">
</form>
<p>Hold down the Ctrl (windows) / Command (Mac) button to select multiple options.</p>
</body>
</html>