The Atacama Cosmology Telescope (ACT) is a new, 6-meter aperture, millimeter-wave telescope that will be located at an altitude of 5200 meters in the Chilean Andes. ACT will be fielded with the Millimeter Bolometric Array Camera (MBAC). The MBAC will incorporate arrays of "pop-up" bolometers using multiplexed Transition Edge Sensors (TES), developed at NASA/GSFC and NIST. The camera will consist of three arrays for multi-frequency ground-based millimeter observations near 150, 220 and 270 GHz. The goal is to map the cosmic microwave background and discover Sunyaev-Zel'dovich clusters. Associated follow-up observations of the clusters will be taken at optical and X-ray wavelengths.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.