The NASA Pacific Exploratory Mission-West (PEM-West) is a major component of the East Asia/North Pacific Regional Study (APARE), a project within the International Global Atmospheric Chemistry (IGAC) program. The broad objective of the PEM-West/APARE initiative is to study chemical processes and long-range transport over the northwestern Pacific Ocean and to estimate the magnitude of the human impact on the oceanic atmosphere over this region particularly for tropospheric ozone and its precursors as well as for sulfur species. The first phase of this mission, PEM-West A, was conducted during September--October 1991. The PEM-West A included intensive airborne measurements of trace gases from the NASA DC-8 aircraft coordinated with measurements at PEM-West A surface sites as well as with measurements obtained from collaborating APARE ground and airborne platforms. This paper reports the experimental design for PEM-West A with a brief summary of the general content and focus of companion papers in this special issue. ¿ American Geophysical Union 1996