A controller (125) for controlling an engine (102) of a vehicle (103) is disclosed, along with a control system (101) comprising a controller (125), a vehicle (103) and a method (200, 500). The controller (125) comprises control means configured to cause stopping of power generation of the engine (102) during movement of the vehicle (103) in dependence on at least one criterion being met and to cause restarting of power generation by the engine (102), in dependence of at least one input signal indicating a requirement for the engine (102) to restart to provide a required power output. The control means is also configured to receive a target engine speed value dependent on a current driveshaft speed and cause the engine (102) to maintain a speed that is no greater than a target engine speed, dependent on the target engine speed value, during a period after receiving the at least one input signal and until a further signal is received indicating that a reconnection of the engine (102) to a driveshaft (104) has been established. The control means is arranged to allow engine speed to exceed the target engine speed after receiving the further signal.