The invention relates to a sheet curl control apparatus including a decurler (350) for reducing the curl in sheet material passing therethrough and adjusting means coupled to the decurler (350) for adjusting the decurling action of the decurler (350). Sensing means (406) in the form of an infra-red emitter (408) and two infra-red detectors (410 and 412 ) are employed for sensing the extent of any residual curl left in the sheet material after it has passed through the decurler (350), and for feeding a signal indicative of the residual curl to control means, conveniently including a stepper motor, for automatically adjusting the adjusting means, for example a rack and pinion arrangement, thereby to alter the decurling action of the decurler (350) in a predetermined manner. The sheet curl control apparatus is described in relation to its use in a copier for duplex copying.