Companies and partnerships (business entities) are basic economic units whose essential feature is profit-making. Their life as well as the life of the society and the state is based on this assumption. Therefore, the regulation model of those entities is very important for development and competitiveness in general. This model imposes appropriate choice and choice ambit of the state regulation and especially appropriate choice of mandatory and default rules, due to the fact that only the later enables freedom of contract and creation of the "societycontract" which is needed in the field of investment. Also, it imposes the choice and its ambit with regard to self-regulation of economic units, on the way of further "society-contract" concept affirmation. On these grounds, the author in this paper deals with the regulation role and its nature, as well as the self-regulation, in the need of dynamic and competitive economy. The author critically analyzes the issue of the legal nature of the business entities and considers that partnerships are, without any doubt, contractual in nature, regardless of the separate legal personality issue, while the limited liability company's nature is both contractual and institutional (which is the main reason for its attractiveness to investors being their oftenest choice) and, finally, that institutional elements dominate in joint stock companies. The author advocates for increasing the number of dispensable business entities legal forms in Serbian Companies Act in order to strengthen the contractual nature of private companies on one hand, and to promote the contract and contractual nature of business entities on the other. The author recommends the introduction of three new legal forms of business entities in Serbian legal life: silent partnership, limited liability partnership and simplified joint stock company and, finally, the introduction of entrepreneur with limited liability (to reduce the risk). Last but not least, having in mind the theory of corporate governance, the concept of company's interest and the legal nature of joint stock companies, the author critically considers broad concession given to the dissenting shareholders and their right to exit the joint stock company which is obliged to buy back their shares. Considering the fact that there is no economic justification for the existing solution, the author proposes the introduction of the new concept of connecting among those rights and the theory of abusing the power of controling shareholeder(s) - theory of abusing the right of majority instead of prescribing nine grounds for using these rights which is currently accepted in Serbian Companies Act.