The primary objective of Ocean Drilling Program (ODP) Leg 203 was to install a cased legacy hole on behalf of the International Ocean Network (ION). ION is engaged in planning, coordinating, and implementing the installation of the Ocean Seismic Network of seafloor geophysical observatories. The site location had been designated by the Dynamics of Earth and Ocean Systems (DEOS) planning effort that was under way at that time in the United States (since subsumed into the U.S. National Science Foundation [NSF] ORION program) and in the United Kingdom, as a site intended for sustained, multidisciplinary observations at and below the seafloor and in the overlying water column. The second objective of Leg 203 was to obtain basement cores, to carry out wireline logging, and to carry out physical, petrological, and paleomagnetic studies of relatively young (11 Ma), unaltered equatorial Pacific oceanic crust. The sites drilled during Leg 203 are representative of those originating in fast-spreading environments. Approximately one-half of the surface area of contemporary oceanic plates originated in the 20% of the global ridge system associated with fast-spreading segments. Prior to Leg 203, only three holes had been drilled during ODP/Deep Sea Drilling Project (DSDP) with penetrations >100 m in such "normal" Pacific crust. The Leg 203 coring and logging goals were intended to add to the limited inventory of baseline data about this understudied, yet common lithospheric setting. All goals identified in the Leg 203 science plan were achieved. A cased legacy hole was installed and cemented in place, providing >100 m of basement penetration, and coring and logging operations were carried out in a second hole, providing 195 m of total penetration, including 85 m of basement.