Research and theorizing on attraction and relationships based on attraction can be traced back almost half a century to a number of lines of research by sociologists and psychologists that could easily be classified as social psychological. Studies of the effects of value and status similarities and of differences in needs or need complementarity dominated the attraction literature during the 1950s and 1960s. Much of the research and theorizing on attraction has concentrated on the early phases of relationship formation to the neglect of the later stages of maintenance or dissolution, although recently there has been an upsurge of interest in the termination of relationships. In addition to the indirect effect of propinquity on attraction through similarity, physical closeness facilitates a number of processes that contribute to attraction. The rewarding internal state of enhanced self-esteem and the reward of approval from others are also involved in generating attraction in still another way.