This chapter examines to what extent ‘history’ can be considered a source of international law. It argues, in a classical way, that history is a material source of international law, though the chapter also examines some norms of positive international law which refer to historical facts. It first casts the question of history as a source of international law in its historical context. Classical international law, with its much greater emphasis on history as a factor of account, stands to by analysed, with reasons for the differences with today investigated. Hereafter, the chapter attends to the main expressions of ‘history as a source’ in the positive international law of today. Finally, the chapter considers the structural effects of historical facts and arguments on the interpreter.