A capillary aerosol generation system comprising: a source of pressurized liquid to be aerosolised; a capillary aerosol generator, and a valve between the source of pressurized liquid and the capillary aerosol generator, the capillary aerosol generator comprising: a capillary flow passage (620,628)(642,646) having an inlet and an outlet; a heater in heat transfer communication with a first zone of the flow passage; a heater in heat transfer communication with a second zone of the flow passage, the second zone being downstream of the first zone; and a controller in electrical communication with the heater for the first zone and with the heater for the second zone, the controller comprising a memory including an instruction set which instructs the controller when to measure the resistance of the heater in a zone, the current through the heater in a zone, the voltage across the heater in a zone, the power consumed by the heater in a zone and/or the temperature in a zone and when to apply voltage to the heater in the first zone, in the second zone or in both, such that the liquid is volatilized and sprayed from a downstream end of the flow passage in the form of an aerosol. a source of pressurized liquid to be aerosolised; a capillary aerosol generator, and a valve between the source of pressurized liquid and the capillary aerosol generator, the capillary aerosol generator comprising: a capillary flow passage (620,628)(642,646) having an inlet and an outlet; a heater in heat transfer communication with a first zone of the flow passage; a heater in heat transfer communication with a second zone of the flow passage, the second zone being downstream of the first zone; and a controller in electrical communication with the heater for the first zone and with the heater for the second zone, the controller comprising a memory including an instruction set which instructs the controller when to measure the resistance of the heater in a zone, the current through the heater in a zone, the voltage across the heater in a zone, the power consumed by the heater in a zone and/or the temperature in a zone and when to apply voltage to the heater in the first zone, in the second zone or in both, such that the liquid is volatilized and sprayed from a downstream end of the flow passage in the form of an aerosol. a capillary flow passage (620,628)(642,646) having an inlet and an outlet; a heater in heat transfer communication with a first zone of the flow passage; a heater in heat transfer communication with a second zone of the flow passage, the second zone being downstream of the first zone; and a controller in electrical communication with the heater for the first zone and with the heater for the second zone, the controller comprising a memory including an instruction set which instructs the controller when to measure the resistance of the heater in a zone, the current through the heater in a zone, the voltage across the heater in a zone, the power consumed by the heater in a zone and/or the temperature in a zone and when to apply voltage to the heater in the first zone, in the second zone or in both, such that the liquid is volatilized and sprayed from a downstream end of the flow passage in the form of an aerosol.