A projection assembly includes a projection system to project a patterned radiation beam onto a substrate, a damping system to dampen a vibration of the projection system, the damping system including an interface damping mass and an active damping subsystem to dampen a vibration of at least part of the interface damping mass, the interface damping mass connected to the projection system, the active damping subsystem including a sensor to measure a position of the interface damping mass, an electromagnetic actuator to exert a force on the interface damping mass, and a controller to drive the electromagnetic actuator based on a signal provided by the sensor, the active damping subsystem including a reaction mass for the electromagnetic actuator to exert a counterforce upon based on the signal provided by the first sensor.