State practice is fundamental to the formation of a custom. It is the material (objective) element of a custom. It is that the States are constantly and uniformly following that practice. But what amounts to a State practice and what constitutes a State practice may cover every activity of the State organs or officials in an international context. It may include treaties, diplomatic correspondence and relations, opinions of national legal advisers, national legislation, policy statements, press releases, official manual on legal questions, executive decisions and practices, decisions of international and national courts, and the practices of international organizations. State practice can be grouped into three categories as evidenced – (a) in the mutual relations among States, (b) in the practice of international organizations, and (c) the unilateral practices of States.