Publisher Summary The study of the structures of biological macromolecules, at atomic level resolution, is usually referred to as “structural biology.” The development of this field and its tools, make a fascinating story—one where new discoveries in physics are rapidly applied to biological systems by intrepid optimists. A notable example is how the heroic efforts of Max Perutz and colleagues led to the first protein structure; this was achieved by interpreting the patterns of spots arising when protein crystals are irradiated with X-rays. Today, new macromolecular structures are appearing at a rate of several hundred per year, and X-ray crystallography has been joined by two other methods capable of giving high resolution 3D structures-electron microscopy and nuclear magnetic resonance (NMR). The results of structural biology are at the core of almost all modem biochemistry—they form the framework on which we hang most other measurements and ideas. The importance of the field has been recognized by the award of a large number of Nobel prizes to its practitioners. Structural knowledge has had a major impact on the understanding of all biological macromolecules and their complexes, including DNA, membranes, and oligosaccharides, but proteins have the most complex structures that are defined precisely by the DNA blueprint.