Icecast is a streaming media project released as a free software maintained by the Xiph.org foundation. It also refers specifically to the server program which is part of the project. Icecast was created in December 1998/January 1999 by Jack Moffitt and Barath Raghavan to provide an open source audio streaming server that anyone could modify, use or tinker with. Alexander Havang was one of the chief architects of this product. Version 2 was started in 2001, a ground-up rewrite aimed at multi-format support (initially targeting Ogg Vorbis) and scaleability.

The Icecast server is capable of streaming content as Vorbis over standard HTTP, Theora over HTTP, MP3 over the protocol used by Shoutcast, AAC, and NSV over the Shoutcast protocol (Theora, AAC, and NSV are only supported in version 2.2.0 and newer.) It uses external programs, called "source clients", to originate the streams, and the Icecast project includes a source client program known as IceS. The source runs typically in the place where the audio is generated (e.g., a studio) and the Icecast server in a place where a lot of bandwidth is available (e.g., a colocation centre).

It has similar functionality to the proprietary media server program SHOUTcast, by Nullsoft.

The main difference between Shoutcast and Icecast Servers is that Icecast has mountpoints, meaning that when a live dj connects, their live stream automatically overrides the playlist stream and when they disconnect, the live stream ends leaving the playlist stream audible once more. Therefore the listeners are not transfered from the autodj to the live stream and then back again as they are with shoutcast.

There are some web sites which give misleading information about this > Like this one <, but the truth is that Shoutcast working with WHMSonic offers an alternative Auto DJ option with an added DJ Manager admin panel thrown in.