In this note, the preview tracking problem, that is, the problem of tracking a reference input when a window of its future values is known, is considered. This is done by showing how the set of all admissible regulated outputs of a system is modified when preview is incorporated. This allows to be seen more clearly the mechanism by which preview allows performance improvement. It also allows preview control systems to be designed using the powerful optimization techniques available for this framework. To exemplify this, some analytical results for the minimum l1, l2 and l(infinity) norms of the tracking error in response to a step reference are derived for a simple system with preview. A worked example of some optimal compensator designs is also presented.