Does a treaty apply to all of a party’s territory? How is territory defined? In the absence of an express definition or other contrary intention, the territory comprises the metropolitan territory of a state and any other territory under its sovereignty. But practice varies. Many bilateral treaties have provisions expressly extending them to overseas territories or enabling such extension by notification or subsequent agreement. Multilateral treaties may also include an express territorial application clause. UK practice from 1967 has been to apply multilateral treaties only to its metropolitan territory unless it makes a specific declaration of extension to any of its overseas territories. On rare occasions, a state may conclude a treaty only so that it applies to a specific overseas territory. The issues posed for federations are discussed, together with certain methods by which the problems can be reduced: territorial clauses, federal clauses and federal reservations. The case of the Hong Kong and Macao Special Administrative Regions is also analysed.