The text has been written as part of the work on the “Social Integration and Collective Identity in Multiethnic Areas of Croatia” project, as a contribution in the setting of the theoretical and hypothetical framework of the research. The paper is divided into two thematic sections. In the first, the authors deal with the issue of the conceptualisation of diverse theoretical approaches to social integration – from the classics of sociology to the most recent discussions – and endeavour to show the manner in which each of them has contributed significantly to the conceptualisation of social integration. The authors draw attention to the “problematic nature”, and also to the “inevitability” of differentiation of the diverse aspects and dimension of integration (social in the narrow sense and also systemic). The second part of the paper includes analysis of national integration as the dominant form of integration in modern societies. In that analysis, the authors support the thesis of a culture of nationalism, which includes the ideas and values of social exclusivism. They also deal with the various challenges confronting national integration today, those that have derived from globalisation and supranational processes, but also those that have their source at local and regional levels. On the basis of the analysis conducted, questions that were hypothetical in nature were posed in the concluding part, which should be answered by empirical research into the contradictions and range of integrational processes in Croatian society.