Social relationships are an essential part of human life. People are social beings who depend on each other for many things. They are
connected to each other and embedded in a network of relatives and non-relatives in all kinds of ways. They are also part of numerous communities they identify
with. By a variety of social contacts people give shape to their social life.
Social relationships have always been an important theme in social science disciplines. Social psychology focuses mainly on the importance of social
relationships for personal functioning. Sociology regards social relationships in the first place as a building stone for society. This chapter presents the leading concepts and theories about social relationships nowadays. We will successively discuss the importance of social relationships for people’s personal lives and their relevance from a societal perspective. We will then describe how the form and meaning of social relationships has changed in the course of time under the influence of social developments. The psychological, social and societal consequences of these change processes will also be discussed. We will then proceed to indicate what it means when people become socially isolated and why social isolation should be seen as a social problem. Thereafter we will look at the main backgrounds and the main approaches of social isolation as described in the literature. Although the importance of social relationships is widely recognized in the social sciences, until now there has been no systematic analysis of the phenomenon of social isolation. For this reason, we will discuss two theoretical approaches that are relevant for a study of social isolation: the network approaches oriented towards various aspects of someone’s network, and the loneliness approaches that emphasize the subjective evaluation of the network. On the basis of these approaches, a definition of social isolation will be formulated in this study. We will end with several conclusions.