Abstract In our review, we introduce an organizational scheme for membrane protein function. It is the relationship between structure, dynamics, and environment that endows the membrane and its constituents with remarkable sensitivity and robustness. Our understanding begins with landmark advances like those presented in the following chapters. Membrane proteins are notoriously difficult to study, and so the work presented here on the ADP/ATP carrier [Nury et al. ( 2 )], rhodopsin [Palczewski ( 24 )], and the cytochrome b 6 f complex [Cramer et al. ( 35 )] represents incredible progress in this now blossoming field.