Intense x-rays from Synchrotron Radiation sources are having an increasingly revolutionary impact on science and technology, and in particular, macromolecular crystallography. Recent research at Stanford University has led to a new x-ray source that will have a major impact on protein structure determination for health care. The Compact Light Source (CLS) is a breakthrough technology that offers a tunable, tabletop x-ray source that could be used like an x-ray beamline at a large light source. The compact size is achieved through the marriage of a laser and a miniature electron storage ring. The photon flux on a sample will be comparable to many synchrotron beamlines. The overall goals of this proposal are to first engineer, then prototype, and finally demonstrate the performance of the CLS. In Phase I, we will test the laser system and design the electron storage ring. In Phase II, we will build the storage ring, integrate the laser system, and demonstrate x-ray production. The CLS will also provide the foundation for future x-ray applications in the health care field. With the CLS, clinical applications such as non-invasive coronary angiography, diffraction-enhanced imaging, and improved cancer detection could be moved from the laboratory into hospitals throughout the nation.