The Code4Lib community is a group of computer programmers and library technologists who largely work for and with libraries. It started as a mailing list in the fall of 2003 when a group of library programmers decided to create an overarching community agnostic towards any particular language or technology. See this email thread (PDF). Soon after the mailing list was created the community decided to setup an IRC channel named #code4lib (originally on Freenode, now on Libera).
In February of 2006 the first Code4Lib conference was held in Corvallis, Oregon, hosted by Oregon State University. Here is the official proposal. This initial Code4Lib conference was a hit, drawing over 80 attendees. The 2007 conference was held on the University of Georgia campus in Athens, GA attracting about 150 attendees. A list of Code4Lib conferences are available on the community website.