A hill holder control system for a vehicle hydraulic braking system in which a valve (1) has an inlet (9) connected to a pedal-operated source of braking pressure and an outlet (10) connected to one or more brake actuators. An inclination sensitive valve member (14) is capable of closing off a valve seat (13b) to trap brake pressure in any brake actuator connected to the outlet and a command means (11, 15, 18, 19) is provided which is operated from an associated clutch pedal and which renders the valve member (14) operative to close off the valve seat when the clutch pedal is operated. The control system also includes a valve member disabling means (31) operable to unseat the valve member (14) from the valve seat (13b) to release any trapped brake pressure, and an electrical control circuit (40) including a "brakes operating" condition sensor (35), a "brakes released" condition sensor (34) and a clutch bite point condition sensor (36). The electrical control circuit (40) is arranged to operate the disabling means (31) when the three sensors (34, 35, 36) indicate the simultaneous presence of all three conditions to ensure a timed release of brake pressure on re-engagement of the clutch.