Canon law was formed as the legal order of the Christian Church during its two thousand years of history since the origins of Christianity in the first century after Christ. Because of its character as religious law, it can be subsumed as a type of sacred law together with Islamic and Jewish law. But when comparing canon law with other sacred laws, we should be aware of its peculiarities. The great sociologist Max Weber (1864–1920) saw its difference from other religious laws in its unique rationality, which he defined as “material rationality.” In Weber’s understanding, this category of rationality meant the orientation of legal traditions toward ethical principles, utility, and political maxims. Weber saw in canon law a guide for secular law on its way to rationality in western legal culture. This evaluation by one of the founding fathers of legal sociology should not be forgotten by legal historians. European legal history, indeed western legal history in general, was influenced by the “two laws,” secular law and canon law. Thus some knowledge of canon law and its principles seems a necessary precondition for a full understanding of the legal heritage of our modern world.