The article is devoted to the review of the problems of formation of the definitive apparatus of law, that is, systems of definitions of categories and concepts of jurisprudence, through which the latter acquire specific meaning within the framework of legal theory or practice. In other words, the definitive apparatus of law is a necessary tool or means of knowing and understanding the relevant legal concepts and categories, and ensuring their certainty. The process of forming legal definitions implies the need to use a variety of methodological techniques, search for relevant information, hypotheses, theories and more. The definitive apparatus of law evolves in connection with a change in both law itself and a number of factors that to some extent influence the process of formation of concepts and their definitions in the legal system. In this regard, the determinants of the formation of the definitive apparatus of law should be sought primarily in those phenomena and processes that directly affect one or another of the content of legal concepts and categories and which are linked, on the one hand, to their more or less static within specific temporal and spatial dimensions, and, on the other, to their substantive diversity, which can manifest even at the level of the most important legal concepts (for example, state, law, legal responsibility etc.). In particular, it should be noted that technological progress has contributed to the emergence of new concepts and definitions that have already become widely used in the system of legislation of modern democratic states (for example, electronic document, electronic digital signature, electronic ticket, electronic settlement document, etc.). Similarly, the development of other spheres and branches of public life, in particular, medicine, business relations, education, etc., necessitates the development of legal definitions of relevant concepts and their consolidation in the legislation in order to ensure more effective legal regulation of social relations. In addition, one cannot ignore the subjective aspect in formulating certain legal definitions, the basis of which is the originality of the outlook of every person, including every scientist. After all, the content of certain concepts and categories, expressed in their definitions, is differently perceived and defined by the relevant subjects, which is determined primarily by their individual characteristics, which include, in particular, personal beliefs, ideals, values, etc. In this regard, we can say that the formation of a definitive apparatus of law is determined simultaneously by a number of objective and subjective factors that determine its specificity and ways and prospects for further development. Therefore, the formation of a definitive apparatus of law should be seen as an integral part of a more general law-formation process, the content of which is linked to those social factors and patterns that affect the development of legal regulation. In this case, the factors of formation of the definitive apparatus of law can be conditionally combined into two groups: internal and external. Internal factors are those facts and circumstances that are determined primarily by the specificity and dynamics of the development of law itself as a socio-normative phenomenon of social reality, and external include those phenomena that are related to the peculiarities of socio-cultural and natural development of society, in particular, with the level of progress of socio-humanities in general, with conditions of functioning of economic, political and other relations, with the content actually prevailing in society and the state ideology, with the specific relationship of law and other social regulators, etc. Keywords: law definitions, the definitive apparatus of law, law, law-formation, law concepts, methodology, law science.