This chapter provides an overview of the LaCoste & Romberg air/ sea gravity meter system which is used for gravity measurements from a moving platform, including but not limited to ships, aircraft, and helicopters. It summarizes the theory behind the gravity meter’s operation as it has been described over many years in the open literature. The chapter attempts to avoid mathematical developments as much as possible. It is concerned with the instrumentation and does not attempt to include a discussion of survey methodology. The principal term in the cross-coupling correction arises because of the arcuate motion of the proof mass in a beam-type sensor. A personal computer controls the gravity meter and erection loops, calculates cross-coupling, filters the data, and logs the data on a suitable storage medium. Attempting to increase the period beyond infinity results in an unstable condition corresponding to a negative period, and the gravity meter beam will tend to seek one stop or the other.