PyCogent is a software library for genomic biology. It is a fully integrated and thoroughly tested framework for: controlling third-party applications; devising workflows; querying databases; conducting novel probabilistic analyses of biological sequence evolution; and generating publication quality graphics. It is distinguished by many unique built-in capabilities (such as true codon alignment) and the frequent addition of entirely new methods for the analysis of genomic data. WWW: http://pycogent.sourceforge.net/