Contract law is the most developed part of Russian civil law and now forms the core of private law relations in the country. The general contract law rules of Russia regulating entrepreneurship are concentrated in the first part of the Civil Code. In turn, the second part of the Civil Code includes the norms regulating different types of contracts, and their provisions usually contain the rules which detail and often make exceptions to the general contract law rules contained in the first part of the Civil Code. Russian contract law is also acquainted with subjective restrictions of freedom of contract. For instance, certain species of contract require that the other party or both parties are entrepreneurs, as, for instance, in retail and supply, or that the other party is a physical person as in the rental of housing premises. Russian contract law is also otherwise based on a particularly high threshold for the change of the contract, considering it as exceptional measure.