Abstract
The diffraction of X-rays by crystals has led to the determination of a very large number of chemical and biological structures. The results underpin theories of chemical bonding as well as revealing a variety of proteins and nucleic acids in three dimensions, and hence their functions. The scope of X-ray crystallography has been transformed by the harnessing of intense, tunable and collimated synchrotron X-ray beams to include higher resolution and more rapid structure determination, as well as studies of structural changes and the determination of the structures of viruses containing up to a million atoms.