Air suspension system

A vehicle air suspension system (10) comprises a source of compressed air (16, 18) coupled to one or more air springs (12, 14). A controller (50) controls flow of compressed air into and out of the air springs. The source comprises a plurality of compressors (16, 18) and the controller is responsive to receipt of signals from the vehicle and/or the air suspension system for controlling the compressors either together as a single unit, or individually, depending on the signals received.