The gradual abandonment of the purely theological basis for religious persecution in favour of a secular posture, based on social and political stability, inevitably led to the emergence of the basic modern premise of freedom of religious worship. The outcome of this long and painful interlude in the history of man becomes apparent when we look at certain recent developments in international law. The unfolding of the modern conception of human rights owes much to the philosophy of such men as Locke. The natural law rights of states produced their distinct natural law echo in the fundamental rights of man. Such ideas played a large part in American and French revolutionary thinking. The right to believe and worship as one likes is now based on natural law conceptions derived from a purely fictitious state of nature and reason. We are prone to say with Sir Henry Maine that natural law theories gave us international law. It is a legitimate extension to go on and say that 18th century natural law theories gave us the idea of fundamental human rights. Among these came, ultimately, freedom in the exercise of religion. It is this parentage that accounts for the provision in the First Amendment to the U.S. Constitution of 1776: ‘Congress shall make no law respecting the establishment of religion, or prohibiting the free exercise thereof’. A like idea translated into law appears in the French Declaration of the Rights of Man of 1789 in providing for freedom from harassment on account of one’s religious opinions.