A device for heating a vapour forming substance includes a compartment for receiving a vapour forming substance. The compartment is divided into plural regions. A heater is provided for heating a vapour forming substance in the compartment in use to generate vapour therefrom. The device further includes means for controlling the heater such that a region adjacent to the heater can be selectively heated and so that vapour from that selectively heated region passes out from the device during operation of the heater. The heater extends in the longitudinal direction of the compartment.