The Boolean multiple attribute, if set, means the form control accepts one or more values. Valid for the email and file input types and the <select>, the manner by which the user opts for multiple values depends on the form control.

Depending on the type, the form control may have a different appearance if the multiple attribute is set. For the file input type, the native messaging the browser provides differs. In Firefox, the file input reads "No files selected" when the attribute is present and "No file selected" when it is not. Most browsers display a scrolling list box for a <select> control with the multiple attribute set and a single line dropdown when the attribute is omitted. The email input displays the same whether or not the multiple attribute is included, but will match the :invalid pseudo-class if more than one comma-separated email address is included if the attribute is not present.

When multiple is set on the email input type, the user can include zero (if not also required), one or more comma-separated email addresses.

<input type="email" multiple name="emails" id="emails" />

If and only if the multiple attribute is specified, the value can be a list of properly-formed comma-separated email addresses. Any trailing and leading whitespace is removed from each address in the list.

When multiple is set on the file input type, the user can select one or more files. The user can choose multiple files from the file picker in any way that their chosen platform allows (e.g. by holding down Shift or Control, and then clicking).

<input type="file" multiple name="uploads" id="uploads" />

When the attribute is omitted, the user can only select a single file per <input>.

The multiple attribute on the <select> element represents a control for selecting zero or more options from the list of options. Otherwise, the <select> element represents a control for selecting a single <option> from the list of options.

<select multiple name="dwarfs" id="dwarfs">
  <option>Grumpy</option>
  <option>Happy</option>
  <option>Sleepy</option>
  <option>Bashful</option>
  <option>Sneezy</option>
  <option>Dopey</option>
  <option>Doc</option>
</select>

When multiple is specified, most browsers will show a scrolling list box instead of a single line dropdown.

Provide instructions to help users understand how to complete the form and use individual form controls. Indicate any required and optional input, data formats, and other relevant information. When using the multiple attribute, inform the user that multiple values are allowed and provide directions on how to provide multiple values, such as "separate email addresses with a comma."

Setting size="1" on a multiple select can make it appear as a single select in some browsers, but then it doesn't expand on focus, harming usability. Don't do that. If you do change the appearance of a select, and even if you don't, make sure to inform the user that more than one option can be selected by another method.

<label for="emails">Who do you want to email?</label>
<input
  type="email"
  multiple
  name="emails"
  id="emails"
  list="dwarf-emails"
  required
  size="64" />

<datalist id="dwarf-emails">
  <option value="[email protected]">Grumpy</option>
  <option value="[email protected]">Happy</option>
  <option value="[email protected]">Sleepy</option>
  <option value="[email protected]">Bashful</option>
  <option value="[email protected]">Sneezy</option>
  <option value="[email protected]">Dopey</option>
  <option value="[email protected]">Doc</option>
</datalist>

If and only if the multiple attribute is specified, the value can be a list of properly-formed comma-separated email addresses. Any trailing and leading whitespace is removed from each address in the list. If the required attribute is present, at least one email address is required.

Some browsers support the appearance of the list of options from the associated <datalist> for subsequent email addresses when multiple is present. Others do not.

When multiple is set on the file input type, the user can select one or more files:

<form method="post" enctype="multipart/form-data">
  <p>
    <label for="uploads"> Choose the images you want to upload: </label>
    <input
      type="file"
      id="uploads"
      name="uploads"
      accept=".jpg, .jpeg, .png, .svg, .gif"
      multiple />
  </p>
  <p>
    <label for="text">Pick a text file to upload: </label>
    <input type="file" id="text" name="text" accept=".txt" />
  </p>
  <p>
    <input type="submit" value="Submit" />
  </p>
</form>

Note the difference in appearance between the example with multiple set and the other file input without.

When the form is submitted, had we used method="get" each selected file's name would have been added to URL parameters as?uploads=img1.jpg&uploads=img2.svg. However, since we are submitting multipart form data, we much use post. See the <form> element and sending form data for more information.

The multiple attribute on the <select> element represents a control for selecting zero or more options from the list of options. Otherwise, the <select> element represents a control for selecting a single <option> from the list of options. The control generally has a different appearance based on the presence of the multiple attribute, with most browsers displaying a scrolling list box instead of a single line dropdown when the attribute is present.

<form method="get" action="#">
  <p>
    <label for="dwarfs">Select the dwarf woodsman you like:</label>
    <select multiple name="dwarfs" id="dwarfs">
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
    </select>
  </p>
  <p>
    <label for="favoriteOnly">Select your favorite:</label>
    <select name="favoriteOnly" id="favoriteOnly">
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
      <option>[email protected]</option>
    </select>
  </p>
  <p>
    <input type="submit" value="Submit" />
  </p>
</form>

Note the difference in appearance between the two form controls.

/* uncomment this CSS to make the multiple the same height as the single */

/*
select[multiple] {
  height: 1.5em;
  vertical-align: top;
}
select[multiple]:focus,
select[multiple]:active {
  height: auto;
}
*/

There are a few ways to select multiple options in a <select> element with a multiple attribute. Depending on the operating system, mouse users can hold the Ctrl, Command, or Shift keys and then click multiple options to select/deselect them. Keyboard users can select multiple contiguous items by focusing on the <select> element, selecting an item at the top or bottom of the range they want to select using the Up and Down cursor keys to go up and down the options. The selection of non-contiguous is not as well-supported: items should be able to be selected and deselected by pressing Space, but support varies between browsers.

• <input>
• <select>
• Allowing multiple email addresses