Windows Media Player (WMP) is a media player and media library application developed by Microsoft that is used for playing audio and video and for viewing images (including subtitles and closed captioning) on personal computers. Windows Media Player replaced an earlier application called Media Player which was introduced in 1991, adding features beyond simple video or audio playback.

In addition to being a media player, Windows Media Player includes the ability to download music and audio content from a computer and copy it to compact disc, burn recordable discs in Audio CD format or as data discs with playlists such as MP3 CD, allowing for convenient file-sharing for uses such as archiving audio material and transcription. Windows Media Player also synchronizes content with a digital audio player or other mobile device, and enable users to purchase or rent music from a number of online music stores.

The default file formats for Windows Media Player are Windows Media Video (WMV), Windows Media Audio (WMA), and Advanced Systems Format (ASF) as well as an XML-based playlist format called Windows Playlist (WPL). The player is also able to utilize a digital rights management service in the form of Windows Media DRM.

Windows Media Player supports playback of audio, video and pictures, along with fast forward, reverse, file markers and variable playback speed. It supports local playback, streaming playback with multicast streams and progressive downloads. Items in a playlist can be skipped over temporarily at playback time without removing them from the playlist. Full keyboard-based operation is possible in the player.

The player includes intrinsic support for Windows Media codecs and also WAV and MP3 media formats. Support for any media codec and container format can be added using Media Foundation codecs. Windows Media Player Mobile 10 on Windows Mobile 6.5 supports MP3, ASF, WMA and WMV using WMV or MPEG-4 codecs.

Windows Media Player features integrated audio CD burning support as well as data CD burning support. Data CDs can have any of the media formats supported by the player. While burning Data CDs, the media can be transcoded into WMA format and playlists can be added to the CD as well.

Windows Media Player features universal brightness, contrast, saturation and hue adjustments and pixel aspect ratio for supported video formats. Windows Media Player can also have attached audio and video DSP plug-ins which process the output audio or video data. The player supports subtitles and closed-captioning for local media, video on demand streaming or live streaming scenarios. Windows Media captions support the SAMI file format but can also carry embedded closed caption data.