Abstract
Today, agency contracts play an important role in the field of domestic and foreign trade. In terms of the formalities of concluding a contract, except for a few countries such as Italy and Egypt, the rest of the countries either follow the principle of consent, agency contracts or consider the condition of being in writing as a positive condition for the occurrence of an agency contract. Therefore, today, legal systems have subtly moved away from the traditional principle of being in writing of contracts. This article has stated in a library manner that despite numerous exceptions to the principle of being in writing of the agency contract, today the principle governing the conclusion of agency contracts is the principle of being in writing of the agency contract, especially in the field of commercial representation. Based on the principle of being in writing, the party who claims to have concluded a contract in a manner other than being in writing must prove his claim. Therefore, mere agreement is no longer sufficient for concluding an agency contract and a positive principle is also needed. This principle of proof has been expressed in different ways in the laws of different countries, and in this article, these methods have been expressed comparatively and the advantages and disadvantages of these methods have been explained in order to be a guide for the legislator who can revise the principle of proof procedures in Iranian law. It should be noted that this principle of proof is different from the traditional principle of formality of contracts and agreements in ancient Roman law.

Keywords: Governing principle, principle of consent of agency, proof or proof procedures of agency contract, comparative law, agency contract,.