The Open Base Station Architecture Initiative (OBSAI) is an industry consortium founded in October 2002 with the goal of producing an advanced base transceiver station (BTS) architecture centered on a set of open internal interface specifications. The goal for standardizing these interfaces is to provide an inherent flexibility to support multiple air interface standards for different RF bands and with different capacity ranges in a common architecture. This paper provides an overview of the OBSAI architecture and specifications developed through the combined efforts of these member companies.