COPYING

SBCL is derived from CMU CL, which was released into the public
domain, subject only to the BSD-style "free, but credit must be given
and copyright notices must be retained" licenses in the LOOP macro
(from MIT and Symbolics) and in the PCL implementation of CLOS (from
Xerox).

After CMU CL was was released into the public domain, it was
maintained by volunteers, who continued the tradition of releasing
their work into the public domain.

All changes to SBCL since the fork from CMU CL have been released into
the public domain in jurisdictions where this is possible, or under
the FreeBSD licence where not.

Thus, there are no known obstacles to copying, using, and modifying
SBCL freely, as long as copyright notices of MIT, Symbolics, Xerox and
Gerd Moellmann are retained.