Cold Spring Harbor Laboratory proposes to continue the course on X-Ray Methods in Structural Biology to be held in the fall of 2012-2016. Crystallography and X-ray diffraction yield a wealth of structural information unobtainable through other methods. This intensive 16-day laboratory/computational course focuses on the major X-ray crystallographic techniques used to determine the three-dimensional structures of macromolecules. The course provides the opportunity for research workers in different biological disciplines to become grounded in the techniques and principles of macromolecular crystallography. It is designed for scientists with a working knowledge of protein structure and function, but who are new to macromolecular crystallography. Topics to be covered include basic diffraction theory, crystallization (proteins, nucleic acids, viruses and complexes), crystal characterization, X-ray sources and optics, synchrotrons, crystal freezing, data collection, X-ray data reduction, multiple isomorphous replacement, multiwavelength/single wavelength anomalous diffraction, molecular replacement, solvent flattening, non-crystallographic symmetry averaging, electron density map interpretation, molecular graphics, structure refinement, structure validation, coordinate deposition, structure presentation along with other relevant topics. The lecturers are chosen on the basis of their contributions to, and knowledge of, the areas covered in the course. In addition, several of the lecturers present their current research to illustrate the principles that are taught in the course. Participants learn through extensive hands-on experiments where they crystallize and determine protein structures, along with lectures and informal discussions on the theory behind the techniques from world leaders in methods development. The course day starts in the morning and runs throughout the day until late at night. There is also a trip to the National Synchrotron Light Source facility at Brookhaven National Laboratory to collect multiwavelength X-ray diffraction data. Applications are open to a wide range of students including advanced graduate students, medical students, post-doctoral fellows, faculty at universities and medical schools, as well as Ph.D. and M.D. scientists from industry. The course is designed to allow students to learn techniques that can be immediately incorporated into their own research. This enables the training of new researchers who can not only solve structures relevant to their field of biological endeavor but also contribute to translational approaches including rational drug design.