This chapter presents the various levels of religions and their significance: from the individual psychological level (What does religion mean for each individual believer?) to the social psychological function of religion in the immediate environment (family, reference group, circle of friends etc.) and on the sociological level, i.e. in societal institutions (schools, associations, churches, unions, parties etc.). It also discusses the significance of belief systems in their respective cultures and how religions have emerged throughout history. In addition, the philosophical and theological levels of religions are also presented.