FLAC (/flæk/; Free Lossless Audio Codec) is an audio coding format for lossless compression of digital audio, developed by the Xiph.Org Foundation, and is also the name of the free software project producing the FLAC tools, the reference software package that includes a codec implementation. Digital audio compressed by FLAC's algorithm can typically be reduced to between 50 and 70 percent of its original size and decompresses to an identical copy of the original audio data.

FLAC is an open format with royalty-free licensing and a reference implementation which is free software. FLAC supports metadata tagging, album cover art, and fast seeking.

Development was started in 2000 by Josh Coalson. The bitstream format was frozen with the release of version 0.9 of the reference implementation on 31 March 2001. Version 1.0 was released on 20 July 2001.

On 29 January 2003, the Xiph.Org Foundation and the FLAC project announced the incorporation of FLAC under the Xiph.org banner. Xiph.org is home to other free compression formats such as Vorbis, Theora, Speex and Opus.

Version 1.3.0 was released on 26 May 2013, at which point development was moved to the Xiph.org git repository.

In 2019, FLAC was proposed as an IETF standard.

In December 2024, FLAC was formally specified in and published as RFC 9639.

FLAC is a lossless encoding of linear pulse-code modulation data.