  Here we describe the Astrophysics Source Code Library (ASCL), which takes an
active approach to sharing astrophysical source code. ASCL's editor seeks out
both new and old peer-reviewed papers that describe methods or experiments that
involve the development or use of source code, and adds entries for the found
codes to the library. This approach ensures that source codes are added without
requiring authors to actively submit them, resulting in a comprehensive listing
that covers a significant number of the astrophysics source codes used in
peer-reviewed studies. The ASCL now has over 340 codes in it and continues to
grow. In 2011, the ASCL (http://ascl.net) has on average added 19 new codes per
month. An advisory committee has been established to provide input and guide
the development and expansion of the new site, and a marketing plan has been
developed and is being executed. All ASCL source codes have been used to
generate results published in or submitted to a refereed journal and are freely
available either via a download site or from an identified source.
  This paper provides the history and description of the ASCL. It lists the
requirements for including codes, examines the benefits of the ASCL, and
outlines some of its future plans.
