  Much of scientific progress now hinges on the reliability, falsifiability and
reproducibility of computer source codes. Astrophysics in particular is a
discipline that today leads other sciences in making useful scientific
components freely available online, including data, abstracts, preprints, and
fully published papers, yet even today many astrophysics source codes remain
hidden from public view. We review the importance and history of source codes
in astrophysics and previous efforts to develop ways in which information about
astrophysics codes can be shared. We also discuss why some scientist coders
resist sharing or publishing their codes, the reasons for and importance of
overcoming this resistance, and alert the community to a reworking of one of
the first attempts for sharing codes, the Astrophysics Source Code Library
(ASCL). We discuss the implementation of the ASCL in an accompanying poster
paper. We suggest that code could be given a similar level of referencing as
data gets in repositories such as ADS.
