This volume covers Leg 59 of the cruises of the Drilling Vessel Glomar Challenger. Of numerous island-arc systems in the western Pacific, the Mariana arc-trench system and the basins and submerged ridges lying west of them in the Philippine Sea were studied because they seemed best suited to answer questions regarding arc-trench and back-arc basin formation. Three years of planning by the JOIDES Active Margin Panel, Ocean Crust Panel, and Planning Committee resulted in a proposed transect of drill sites aligned more or less along the 18th parallel. This South Philippine Sea transect was designed to investigate each major basin and ridge between the central part of the West Philippine Sea and the Mariana Trench and the Pacific Ocean plate immediately to the east. DSDP Legs 59 and 60 were designated to undertake the study; the drilling program was conducted during the period February 3 through May 15, 1978. Leg 59 drilling program comprised Sites 447 through 451 and the Leg 60 program Sites 452 through 461. Leg 59 sailed from Naha, Okinawa Japan to Apra, Guam.