The three volumes in Methods in Molecular Biology covering Physical Methods of Analysis (vol. 1, Spectroscopic Methods and Analyses: NMR, Mass Spectrometry, and Metalloprotein Techniques; vol. 2, Optical Spectroscopy and Macroscopic Techniques; vol. 3, Cryst- lographic Methods and Techniques) differ from others in this series in several ways. Each volume covers a group of techniques for the char- terization of biological molecules and their interactions that involve the application of modern techniques of physical chemistry. These techniques by and large do not lend themselves to the hands-on approach and cannot usually be carried out by the molecular biologist alone, but most often require collaboration with a specialist. The biologist or biochemist contemplating such a collaboration may feel somewhat at a distance from the experimental work and further isolated by the use of the jargons of analytical and physical chemistry. Physical methods have been used in molecular biology from the earliest days, from simple applications of optical spectroscopy to the complexity of X-ray crystallography, and the full range of these me- ods will be covered over the three volumes. The methods dealt with in this first volume have largely developed from beginnings in small molecule chemistry to the point where they play a valuable role in the characterization of biological macromolecules.