A series of small- to intermediate-sized spacecraft that is the centerpiece of NASA's Earth Science Enterprise (ESE). Planned for launch beginning in 1999, each of the EOS spacecraft will carry a suite of instruments designed to study global climate change. ESE will use space-, aircraft-, and ground-based measurements to study our environment as an integrated system. Designing and implementing the ESE is, of necessity, an international effort. The ESE program involves the cooperation of the U.S., the European Space Agency (ESA), and the Japanese National Space Development Agency (NASDA). The ESE program is part of the U.S. interagency effort, the Global Change Research Program.