To understand the essence of a legal system, one of the priority tasks is to study the doctrine of its sources of law. The situation with Islamic law is similar. The doctrine of sources of law is one of the most developed because it has been studied by a large number of lawyers and orientalists. At the same time, we see insufficient research on this doctrine due to a large number of approaches to understanding the term «source of law». In this paper, we have explored the sources of Islamic law in accordance with the Twelvers madhhab, as it is a basic school of Shiite legal doctrine.As a theoretical basis for the analysis of approaches to understanding the «sources of law», we have chosen approaches and their characteristics that would correspond to current approaches to the study of legal phenomena and processes in domestic legal science. Thus, the sources of Shiite Islamic law were analyzed in accordance with the following dominant approaches to understanding the meaning of the term «source of law»: epistemological (source of law is defined as a source of knowledge of the law, ie where we get our knowledge of the law. Most often it is legal monuments of history); material (social relations in general, natural, cultural, political, religious and other factors that determine the emergence, development and content of law); institutional (the law-making activity of state authorities and civil society institutions that establish or sanction legal norms); ideological (legal ideas, concepts, legal awareness of the subjects of lawmaking, which form a certain legal understanding and are the basis of the rules of law, affect their content); formal-legal (various forms (methods) of external expression of legal norms). After analyzing different approaches, we came to the conclusion that depending on the approach, the sources of Shia Islamic law are:according to the classical approach (ie, which is followed by Muslim scholars of Islamic law) - the Quran, Sunnah, ijma, akl;according to the epistemological approach - the Quran, Shia collections of hadiths «Al-Kafi» Kulaini, «Man la yahduruhu-l-faqih» by Sheikh Saduk and others), the works of prominent lawyers «az-Zaria» by Seyid Murtaza, «al-Nihai» by Sheikh Tusi);according to the material approach - social relations, cultural, religious and political factors;according to the institutional approach – religious scholars and faqihs, partly the new Islamic states;according to the ideological approach - God (and His will), akl (intellect, reason);according to the formal-legal approach - the Quran, hadiths from the Prophet and Imams, legal doctrine