A rotary electromagnetic actuator includes a biasing assembly for applying a torque to its rotor. Such an actuator may be used to operate a poppet valve of an internal combustion engine. The biasing assembly is switchable between (a) a first configuration in which the biasing assembly exerts a torque on the rotor over at least part of the range of rotation of the rotor, wherein the torque exerted varies with the rotational position of the rotor according to a torque profile, and (b) a second configuration in which the biasing assembly exerts substantially no torque on the rotor over the range of the rotor.