Flag State jurisdiction provides one of the principal ways of maintaining legal order over activities at sea, although its significance has lessened as a consequence of extensions in coastal State jurisdiction over ocean spaces. Any State may grant to a ship the right to sail under its flag. The flag State then enjoys primary legislative and enforcement jurisdiction over its ships on the high seas, subject to some limited exceptions. Ships located within coastal waters are subject to a more sophisticated combination of flag State and coastal State jurisdiction. The basic parameters of jurisdiction are set forth in the 1982 United Nations Convention on the Law of the Sea (LOSC), although other instruments develop how such jurisdiction is to be exercised in the context of specific activities such as navigation and fishing. One of the most fundamental concerns facing the law of the sea is the ability and willingness of flag States to exercise effective control over ships flying their flag. This has resulted in attempts to secure better flag State compliance with their responsibilities, as well as provoking the development of alternative models of control, such as port State control. These factors pull towards more sophisticated models of regulation. Accordingly, a more careful and holistic view of jurisdiction is essential to understanding how order is maintained at sea.