This book formulates an evolutionary and pluralistic view of social systems in the global age, especially with reference to Niklas Luhmann's theory of social systems. Several paired concepts, such as national society/world society, stratification/functional differentiation, diffuse/specific, universalistic/particularistic, and inclusion/exclusion, illustrate the transformation of social structure and its effects on the constructive principles of social systems and the definition of individual identity. Every functional subsystem has become more autonomous and the socio-cultural sources of individual identity have become more diversified than in the past. The book proposes the concept of the "intermediary unit" and discusses its significance and relevance in the social systems theory. In the background of this discussion, the reality is that there is no system of meaning and values that are valid in all areas of the world society that has emerged in the process of functional differentiation and globalization, nor can we design such a system theoretically. The significance of intermediary units is considered; the competition of intermediary units and meaning-value spaces in the actual social process is defined as the politics of meaning; and a new form of pluralism based on the concept of polycontexturality is proposed. These factors seem to make the whole world more and more complex, risky, uncertain, and nontransparent. The evolutionary and pluralistic design principles of social systems including various intermediary units improve our capacity to cope with future risks.