Relations between Cameroon and the African Union (AU) have always been characterized by a certain form of singularity deriving from the nature of the organization, the status of Cameroon within it, and the conception that Cameroon has had and Continues to have its role on the African scene. Cameroon has this peculiarity of applying with a certain ease, a resolutely realistic approach to the African system. The realistic approach translates into a permanent quest for Cameroon's position on the African scene, a strict and traditional defense of the national interests of the country. Cameroon's foreign policy constantly refers to the promotion of values and principles dear to the African Union. Indeed, the problem that arises in this case is that states such as Cameroon can not fulfill some of their regalian functions and are consequently powerless vis-à-vis newcomers Challenges. Given that they do not necessarily present themselves as temporary phenomena, but often, such as the growth of poverty or environmental degradation, which are far more durable, the strengthening of regional structures should therefore make it possible to compensate for these shortcomings in the longer term. A different approach to explain the relevance of the cooperation between Cameroon and the African Union is presented by the authors grouped in the institutionalist current. Starting from an anarchic conception of the world, comparable to that of the realists, institutionalists see the role of co-operation essentially in that it leads to reducing uncertainties, and hence mistrust between states. According to Robert Keohane, international institutions would be defined as "persistent and connected sets of rules (formal and informal) that prescribe behavioral roles, constrain activity, and shape expectations"(Keohane, R-O: 1989). In this perspective, regionalism can be seen as a more or less direct result of the security dilemma assumed by realistic authors. In this context, the African Union, by its nature and its place given to Cameroon, offers it an important framework for expression. In its normative and operational dimension of promoting the values of peace, it defends an agenda that has a particular resonance with Cameroon. The African Union is simultaneously the forum for the dissemination of the "universal message" of Cameroon and this key vector that allows it to hold its rank. Such an analysis is of particular relevance during the first seventeen (17) years of existence of the AU. Cameroon, even after ratifying the Constitutive Act of the AU, has kept its line of foreign policy adopted for years. This foreign policy of Cameroon is based on the following points: the principles of national independence in accordance with the Charter of the United Nations, cooperation and African unity, non-alignment, the importance of the development imperative And pacifism. It is clear that the analysis of the relationship between a State and an international organization is first of all viewed from a legal and politico-diplomatic standpoint. However, this analysis will also focus on the economic and social aspects of these relationships. The subject involves the analysis of the relations between a State and an intergovernmental organization of a regional character. More specifically, it is a question of studying the mutual relations between Cameroon and the African Union.