A lithographic apparatus, comprising: a programmable patterning device, configured to provide a plurality of radiation beams; a projection system (12, 14, 18), configured to project the plurality of radiation beams onto a substrate to form respective spots of radiation; and a radiation spot measurement system, comprising: a target, onto which the spots of radiation may be projected for a spot measurement process, the target comprising a measurement target; a radiation detector, configured to detect radiation from one of the spots of radiation that has been projected onto the measurement target; and a controller, configured to receive information from the radiation detector and, based on the information, to determine at least the position of the spot of radiation relative to an intended position of the spot of radiation on the target in a plane substantially parallel to an upper surface of the target; characterized in that the target is elongate and comprises a plurality of the measurement targets, distributed along the target in its elongate direction; and the lithographic apparatus comprises an actuator system configured to control the position of the radiation detector relative to the target such that, at different respective positions, it can detect radiation that has been projected onto different measurement targets on the target. a programmable patterning device, configured to provide a plurality of radiation beams; a projection system (12, 14, 18), configured to project the plurality of radiation beams onto a substrate to form respective spots of radiation; and a radiation spot measurement system, comprising: a target, onto which the spots of radiation may be projected for a spot measurement process, the target comprising a measurement target; a radiation detector, configured to detect radiation from one of the spots of radiation that has been projected onto the measurement target; and a controller, configured to receive information from the radiation detector and, based on the information, to determine at least the position of the spot of radiation relative to an intended position of the spot of radiation on the target in a plane substantially parallel to an upper surface of the target; characterized in that the target is elongate and comprises a plurality of the measurement targets, distributed along the target in its elongate direction; and the lithographic apparatus comprises an actuator system configured to control the position of the radiation detector relative to the target such that, at different respective positions, it can detect radiation that has been projected onto different measurement targets on the target. a target, onto which the spots of radiation may be projected for a spot measurement process, the target comprising a measurement target; a radiation detector, configured to detect radiation from one of the spots of radiation that has been projected onto the measurement target; and a controller, configured to receive information from the radiation detector and, based on the information, to determine at least the position of the spot of radiation relative to an intended position of the spot of radiation on the target in a plane substantially parallel to an upper surface of the target; characterized in that the target is elongate and comprises a plurality of the measurement targets, distributed along the target in its elongate direction; and the lithographic apparatus comprises an actuator system configured to control the position of the radiation detector relative to the target such that, at different respective positions, it can detect radiation that has been projected onto different measurement targets on the target.