The problem of the antimonopoly regulation and stimulation of the development of competition is becoming more and more acute for our country. The principal point of difficulty in the antimonopoly regulation of the companies’ activities on the market is the poorly developed competition legislation and heavily monopolized regional markets. One of the ways of solving these problems is borrowing some pro-competitive approaches and legislation that have been developed and successfully implementing in the countries with the developed open market economy with free competition, particularly in the EU In general, the EU rules on competition applying to undertakings include a general prohibition on cartels that results in the nullity of prohibited agreements or decisions, but that is made less harsh by the possibility of exemption (Article 81), a prohibition on the abuse of dominant positions (Article 82). However, the article is dedicated to analyzing of the most important and at the same time very controversial terms and meanings that are used in the EU competition legislation. These terms are set out in the Article 81(1) of the Rome Treaty establishing the European Community (EC Treaty). In particular this article considers the following:1. conception of “undertaking” in terms of the competition law;2 meaning “agreements, decisions of associations and concerted practices”;3 meaning “which may affect trade between member states”;4 meaning “which have as their object or effect the prevention, restriction or distortion of competition within the common market”.