Published by the American Geophysical Union as part of the Geophysical Monograph Series, Volume 123. In recent years, two separate geophysical research cultures have developed in the United States to study the atmosphere: one of space scientists, who focus on the mesosphere, thermosphere and ionosphere, and the other of atmospheric scientists, who focus on the troposphere and stratosphere. The boundary between these two research domains roughly coincides with the stratopause (50 km). While the division ofthe atmosphere into layers and boundaries serves as a useful way to characterize the various chemical and dynamical processes that distinguish these layers, these boundaries are not impermeable. To understand such critical issues as global change, geophysicists must study the atmosphere as an integrated system. The purpose of this monograph is to highlight those studies that consider the coupling of these two regions and thus bring together two scientific specialties (atmospheric science and space science) that are often considered separately.