The focus of this article is the problem of polycontextuality and the unity of society. It bases on the system theory and emphasizes its character as a theory of differentiation. This article explores the following points: First of all, the author will distinguish between the social system and the psychological system. Secondly, the author will define communication as basic unit of the society. The author also asserts that the society is what communications arrive, and that the society is not arrived by communications. In other words, the society is only a self-description of the society that exists as a theme in the communications. Thirdly, the author asserts that the modern society is a functional differentiated society and that the polycontextuality is not other than its necessary result. No concept of the unity of society is exclusively correct under these conditions. The possibility of the social order must also be observed under these conditions. The mutual limitation of the functional subsystem of society can better explain the integration of society than the theory of normative integration. The concepts of the unity of society compete with each other in the explanation of the result of the functional Differentiation and the polycontextuality in the semantic level.