This comprehensive volume, written by experts in the field, brings together a coherent set of reviews of different biophysical methodologies for the study of reversible protein interactions. These reviews allow the reader to gain a deep understanding of the biophysical observables, to stimulate creative thought on how the techniques may be applied to study a particular biological system, and to foster collaboration and multi-disciplinary work. The side-by-side presentation of different approaches highlights aspects they have in common, as well as orthogonal viewpoints that may provide opportunities for synergistic combination. Protein Interactions is an ideal book for biochemists, protein scientists, bioenginners, and molecular and cellular biologists.