Major sources of international law include treaties and decisions of international tribunals, documents from international and regional organizations, and material on selected topics. A treaty (sometimes called a convention, covenant, protocol, charter, pact, etc.) is an agreement between two or more nations or international organizations. It may be bilateral (between two countries), or multilateral (between three or more countries). The treaty text may provide for the manner by which it takes effect. Often, the agreement will enter into force when it has been signed and ratified by a certain number of parties.