However the antitrust legislative text more known and influential is the Sherman Act, instituted in 1890, in the United States, that are born initially as well it detaches Salomo Son, the central concern of the Law of Sherman were the protection of the consumer in face of the extreme one to be able economic in the market. Concern with practical the disloyal ones of the excessively competing ones was still not had (2002, P. 63). However in a stage that if followed, transferred to apply it the rule of illegality to the practical monopolistas and oligopolistas in the figures of cartels, monopolies and holdings trying to guarantee the free competition thus and is in the creation of this law that appears the Concorrencial Right. 2. Monopoly, a conceptual vision. Monopoly is a word of origin Greek, who means ' ' to vender um' ' , monos (one) and polein (to vender), it is characterized for an imperfect competition, instead of having a great number of small companies, possesss only one responsible great firm mainly for the valuation of prices and the fact not to exist competing what valley is the price fixed for the monopolista company.

Amongst the main characteristics it can be detached: one only company; she does not have substitute products; she does not have competitors; the company has considerable control of price; is practically impossible the entrance of another company in the market. How much to this it detaches Mendes: The curve of demand of the market and the curve of demand of the firm, in monopoly situation, are one only. While one firms in a competitive market, its production for price can vender all the same, the monopoly can increase the sales if reduce the price of its product. Thus, the prescription delinquent of the monopolista and the demand are two different curves, and are the root causes of the inefficient allocation of resources in this type of market.