Book excerpt: Gramicidin channels have been studied intensively for more than 25 years. They serve as model transport systems for large protein ion channels, since it is difficult to glean high-resolution structural information on the latter. This book includes contributions from virtually all the major scientists studying gramicidin channels and is the only compilation of work in this field. It discusses crystallographic, spectroscopic, electrophysiological and computational studies, especially in the light of the recent availability of high-resolution structural data, and it compares these with insights derived from larger systems. As well as drawing together much new and exciting work in this field, it provides pointers to promising new research directions.