RSS enclosures are a way of attaching multimedia content to RSS feeds by providing the URL of a file associated with an entry, such as an MP3 file to a music recommendation or a photo to a diary entry. Unlike e-mail attachments, enclosures are merely hyperlinks to files, the actual file data is not embedded into the feed (unless a data URL is used). Support and implementation among aggregators varies: if the software understands the specified file format, it may automatically download and display the content, otherwise provide a link to it or silently ignore it.

The addition of enclosures to RSS, as first implemented by Dave Winer in late 2000 [1], was an important prerequisite for the emergence of podcasting, arguably the most common use of the feature as of 2010^[update]. In podcasts and related technologies enclosures are not merely attachments to entries, but provide the main content of a feed.

In RSS 2.0, the syntax for the <enclosure> tag, an optional child of the <item> element, is as follows: