Each chapter of this volume is based on a presentation at the international Theoretical Institute, "Interactions among Physical, Chemical, Biological, and Geological Processes in Back-arc Spreading Systems", which was jointly sponsored by Ridge 2000 and InterRidge, on Jeju Island, South Korea, in May 2004. The volume is divided into two sections. Papers in the first section synthesize the state of knowledge of back-arc basins in general, from the perspectives of a broad range of disciplines. The papers are arranged according to their subject matter, roughly following the flow of energy and material from their origins in the mantle, through the magmatic systems that create and modify the oceanic crust, to the hydrothermal and biological systems that derive their existence from magmatic heat and chemicals. Papers in the second section are case studies, focused on the geology and geophysics of individual back-arc basins. These include two back-arc systems that are more than usually complex, as a result of their more complex tectonic settings.