Subjective aspect plays important role in the regulation of economic activity. The basic problem in this respect concerns the definition of an entity which carries on business. The article is an attempt to submit comments to the legal solutions for businesses, included in the Law on Freedom of Economic Activity. In this regard, the paper analyses legal regulations of such normative acts, as the Law on the Business (the concept of the business entity) and the Act of Business Law, which were in force in Poland since the late eighties until the entry into force of the Law on Freedom of Economic Activity. The author also drew attention to the concept of merchant and the enterprise as legal institutions, occurring earlier in the Polish legislation. The article comprehensively discusses types of entrepreneurs. In this respect, it presents the problem of natural persons, legal persons and organizational units without legal personality (the flawed legal persons). Much attention is devoted to the presentation of commercial companies' issues (partnerships and associations of capital). The paper also explains aspects connected with running a business or professional activity by the entrepreneur in his own behalf. In addition to examining the development of normative acts in the Supreme Court, the author used the judgement of Supreme Court and the Supreme Administrative Court, and views of doctrine.