The Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment was conducted during February--March, 2000 to study the evolution of tropospheric chemistry at mid to high latitudes over North America. The experiment used airborne in situ and remote sensing measurements of trace gases, radiation, and aerosols, combined with model simulations, to describe the major processes that control evolution of ozone and oxidants during the winter-spring transition. This paper introduces the major scientific questions of the TOPSE experiment, describes the conduct of the mission, and introduces the scientific results discussed in a series of companion papers in this special section. Among the significant findings of the experiment was that tropospheric ozone increases from winter to spring were dominated by in situ photochemical production in the troposphere, rather than by transport from the stratosphere. Also unique observations of widespread surface ozone depletion events, and of seasonal evolution of trace gases and aerosols as a function of latitude and altitude, were obtained over the course of the mission.