A head-mountable display system comprises a head mountable display having a frame to be mounted onto an observer's head, the frame defining one or two eye display positions which, in use, are positioned for viewing by the observer. The frame comprises one or more shutters for obscuring the observer's view of the surrounding real environment and a display element mounted with respect to each of the eye display positions. The display element provides a virtual image of a video display of a video signal from a video signal source to the observer. An object detector detects the presence of an object within a detection range of the observer's head. And a controller controls operation of the head mountable display so as to allow the observer to view at least a portion of the surrounding real environment in response to detection of the presence of an object within the detection range.