Abstract: A trailer braking system including one or more trailer wheel assemblies having conventional hydraulically-actuated shoe or disc brakes; a conventional brake master cylinder mounted on the trailer to provide pressurized hydraulic fluid to the wheel cylinders to actuate the brakes; an electric solenoid mounted on the trailer to drive the piston of the master cylinder, preferably through a force-multiplying lever arm, in response to an electrical braking signal from the towing vehicle; and a controller to generate a braking signal proportional to the amount of braking force desired in the trailer brake. The controller may be connected to, and follow the movement of, an element of the towing vehicle's braking system, such as the brake pedal or the vehicle master cylinder piston rod, or the controller may be manually actuated by an operator. There is a manual parking brake which can maintain the force exerted on the wheel cylinder by the trailer master cylinder when power to the solenoid is shut off.