The importation into or transplantation of elements of the modern world onto the Iranian society has left an impact on all aspects of individual and social life in the country. To analyze and tackle those problems in the normative and legal fields heavily depends on a deep understanding of modernity and its effect on religious law. On this basis, it is an imperative to provide an answer to three questions. First, what were the grounds of the emergence of modernity in the West? Secondly, what were the constitutive elements of modernity? Thirdly, what kind of changes did modernity bring about in the traditional legal system, or what were the characteristic features of the modern law? It will be shown that modernity, on this account, made the law change in four directions. They are the "aim" and "source" of law, the legal "method" and the "competent legislature" within the legal system.Modern law came out of interactions embedded in modern life, on one side, and its existence provided for and guaranteed the survival of that life, on the other.