The multilateral convention on the demilitarization and neutralization of the Åland Islands was concluded in 1921 and the Convention is still in force. This book analyses the regime of navigation in the territorial waters of the Åland Islands in relation to the Convention on the Territorial Sea and the Contiguous Zone, and the United Nations Convention on the Law of the Sea (UNCLOS). The work discusses the right of entry into internal waters in regard to the 1921 Åland Convention and domestic legislation. It examines the historical concept of innocent passage and presents its application in the territorial waters in the Åland Islands. The United Nations Convention on the Law of the Sea provides a special regime for straits used for international navigation. The study analyses the regime of transit passage and the right of innocent passage, both of which apply to international straits. However, the United Nations Convention on the Law of the Sea exempts those straits “in which passage is regulated in whole or in part by long- standing international conventions in force specifically relating to such straits” (Article 35(c)). UNCLOS does not indicate to which straits this provision applies, but Finland and Sweden have classed the Åland Strait according to this category. This work analyses the applicability of Article 35 (c) to the Åland Strait and presents its comparability to other straits mentioned in the course of the Third Law of the Sea Conference.