Thanks to the Veterans Health Administration and WorldVistA member contributions there is a rich library of publicly available documentation for VistA.
WorldVistA Wiki - a continuously improving library of valuable documentation describing how to install and configure VistA as well as other VistA related subjects.
VistA Monograph - provides an overview of VistA functionality and architecture.
VistA Documentation Library (VDL) - a repository of VistA application, user and technical manuals.
The Standards and Conventions document from 2008 (last revised in Feb. 2011) from the VA's SACC.