A readily reproducible collection of established and emerging techniques for studying the interaction between proteins and ligands, including biochemical/bulk techniques, structure analysis, spectroscopy, single-molecule studies, and theoretical/computational tools. Among the highlights are surface plasmon resonance (SPR) and reflectometric biosensor approaches, high-throughput screening with confocal optics microscopy, single molecule fluorescence and fluorescence correlation spectroscopy (FCS), atomic force microscopy (AFM), crystallography of reaction intermediates, and time-resolved x-ray crystallography. The protocols follow the successful Methods in Molecular Biology(t) series format, each offering step-by-step laboratory instructions, an introduction outlining the principle behind the technique, lists of the necessary equipment and reagents, and tips on troubleshooting and avoiding known pitfalls.