The progressive evolution of the South Philippine Sea island arc-back-arc complex deduced from drilling on Glomar Challenger Leg 59 places significant restraints upon tectonic processes that may operate in convergent plate boundaries characterized by back-arc spreading systems. As previosuly recognized, remnant arc precursors of the modern Mariana arc and intervening back-arc basins progressively developed from west to east to form the Palau-Kyushu Ridge, the Parece Vela Basin, the West Mariana Ridge, and finally the modern Mariana Trough and Mariana arc. New data suggest that initial periods of back-arc spreading are coincident with minimal arc volcanism rather than major periods of arc volcanism as previously suspected.