The article analyzes the scientific approaches to the definition of "investment", which are reflected in the foreign and domestic economic and legal literature. Four scientific schools have been identified: Western European, American, Russian and Domestic, each of which has demonstrated its own approaches to addressing the identified scientific issues. The legislative definition of the category is determined, which fixed in the domestic normative legal acts. It was stated that there is no single approach to the essence and content of the concept of "investment". Regulatory legal acts of different legal force provide different interpretations of the definition, while other legislative acts generally avoid, do not provide an appropriate interpretation. Such a state of regulatory provision not only generates discussions among scientists, but also does not create favorable conditions for the practical sphere of investment activity. Based on the analysis of the norms of domestic and international law, taking into account the achievements of the economic and legal scientific heritage, the author's concept of "investment" as an investment in objects of entrepreneurial and / or other economic activity as property and / or property rights is proposed for the purpose of obtaining income (profit, interest ), not excluding, however, the possibility of achieving an additional socially significant beneficial effect. The necessity of unification of the concept of "investment" in the domestic normative - legal acts and bringing it in line with the norms of the European legislation is emphasized. The process of improving the legislation about investment activity should be based on scientific achievements, that was emphasized. It is concluded that the unification of the concept of "investment" will avoid arbitrary, voluntarist interpretation of it and clearly identify those areas of improvement in which the latest Ukrainian investment legislation should move.