The NCI/NIGMS Synchrotron X-ray Crystallography Beamline provides dedicated access for NCI researchers to a state-of-the-art synchrotron X-ray beamline for determining cancer relevant macromolecular structures using X-ray crystallography. NCI has partnered with the National Institute of General Medical Sciences (NIGMS) to fund the construction and management of a state of the art macromolecular crystallography synchrotron beamline for determining structures of biologically important macromolecules. The beamline, GM/CA CAT, is located at the Advanced Photon Source (APS) on the grounds of Argonne National Lab (ANL) just outside of Chicago. This facility has three experimental stations, two with insertion devices (ID's) and one with a bending magnet (BM) that can accommodate the experimental demands of virtually any crystallography project. With computerized automounting and crystal testing the facility can handle a large number of experiments in a typical 8 hour user slot. Currently the beamline has microfocus capabilities down to 10 microns. Computerized auto location and rastering make this the ideal facility for small crystals, crystals susceptible to radiation damage, and crystals with variable mosaicity or twinning. Kappa geometry and a long detector translational axis make this facility ideal for extremely large unit cells and unit cells with odd dimensions. The ID's are tunable across an extremely broad energy range and can accommodate almost any multi-wavelength anomalous dispersion (MAD) experiments.