The ALMA Test Facility (ATF) serves two purposes: it is the test bed upon which the ALMA prototype antennas are evaluated and it serves as a platform for ALMA prototype instrumentation and software testing. Each of the two prototype antennas have been evaluated using a uniform set of criteria which gauge their relative performance. The evaluation of the two ALMA prototype antennas concluded in May 2004. A third prototype antenna, built by Mitsubishi, is also located on the ATF site. The National Astronomical Observatory of Japan (NAOJ) is evaluating this antenna as a potential prototype for the Atacama Compact Array (ACA), a possible enhancement to ALMA.