LAME is an open source MP3 (that is, MPEG-1 audio layer 3) audio compression application. LAME is a recursive acronym for LAME Ain't an MP3 Encoder, although the current version is a stand-alone encoder.

LAME is a research project for learning about and improving MP3 encoding technology. The LAME software includes an MP3 encoding library, simple front-end application, an enhanced psycho-acoustic model (GPSYCHO), and a graphical frame analyzer (MP3x).

The open source development model of LAME allows improving its quality and speed since 1999. It is now a highly evolved MP3 encoder, with quality and speed able to rival state of the art commercial encoders.

However, commercial use of LAME (including the LAME encoding engine in a free encoder) requires a patent license from Thomson Multimedia.

LAME produces the highest quality MP3 files for (average) bitrates of 128 kbit/s and higher. In a public listening test early in 2004, 128 kbit/s LAME MP3 files were the least detectable when compared to uncompressed audio.

Previously, LAME was simply a set of patches against the ISO demonstration source, which is distributed separately, hence the "Ain't an Encoder" name. That ISO code had a restrictive license but was available free of cost. However, in May 2000, the LAME project reimplemented the last of the ISO source code, and now LAME is a new implementation available under the LGPL license.

In spite of its name, LAME is perhaps the best free MP3 encoder available today.