A differential control system for the center and rear differentials of a four-wheel-drive vehicle comprises a controller (28) which receives signals input from a number of sensors including ride height sensors (42, 44, 46, 48). The controller (28) determines from the ride height signals the degree of articulation of the vehicle suspension and controls the degree of locking of the differentials in response. The degree of locking is increased with increased articulation, and with increased rate of change of articulation.