Over the last 15 years, since the discovery of the T cell receptor gamma and delta genes, rapid progress has been made toward the understanding of the biology of gamma-delta T cells. They differ from conventional alpha-beta T cells not only in T cell receptor composition, but also in their development, tissue distribution, and physiological functions. This volume contains seven chapters contributed by experts on different aspects of gamma-delta T cells, including the natural ligands for gamma-delta T cell receptors, IL-7-dependent regulation of gamma-delta T cell development, cytokine-mediated intercellular communication of gamma-delta T cells with other cell types, and their physiological functions in innate and adaptive immune responses. The comprehensive review articles collected in this volume will be of interest to basic immunologists who wish to update their knowledge on the biology of gamma-delta T cells. The book also provides a unique opportunity for non-immunologists and clinicians to understand how the immune system is specifically equipped to protect the body against pathogens at the environmental interface.