musl as a whole is licensed under the GNU LGPL version 2.1 or later. See the file COPYING for the text of this license. See below for the copyright status on all code included in musl: The TRE regular expression implementation (src/regex/reg* and src/regex/tre*) is Copyright © 2001-2006 Ville Laurikari and licensed under the terms of the GNU LGPL version 2.1 or later. The included version was heavily modified in Spring 2006 by Rich Felker in the interests of size, simplicity, and namespace cleanliness. Most of the math library code (src/math/*) is Copyright © 1993 Sun Microsystems, Inc. Some files are Copyright © 2003 Steven G. Kargl and labelled as such. All have been licensed under extremely permissive terms which are compatible with the GNU LGPL. See the comments in the individual files for details. The implementation of DES for crypt (src/misc/crypt.c) is Copyright © 1994 David Burren. It is licensed under a BSD license compatible with the GNU LGPL. All files which have no copyright comments are original works Copyright © 2005-2011 Rich Felker, the main author of this library. The decision to exclude such comments is intentional, as it should be possible to carry around the complete source code on tiny storage media. All public header files (include/*) should be treated as Public Domain as they intentionally contain no content which can be covered by copyright. Some source modules may fall in this category as well. If you believe that a file is so trivial that it should be in the Public Domain, please contact me and, if I agree, I will explicitly release it from copyright.