Social scientists from different disciplines have conducted research on relationships. The list includes psychologists (e.g., social, developmental, clinical, cognitive, counseling), sociologists, anthropologists, and health scientists. Different disciplines employ various approaches to address relationships. For instance, social psychologists seek universal properties in human relations. Sociologists, on the other hand, pay much attention to changes in family ties and social connections and how social structures and contexts (e.g., social class, race, gender, norms, and social policy) impact these relationships. Relationships have been a central research concern in sociology. Sociologists have been particularly interested in studies of intimate relationships, such as marriage and other familial ties. In sociology, social relationships are divided into primary and secondary groups. Primary ties are characterized by direct, personal, and intimate interactions. In addition, primary group members exchange tacit items such as support, love, and concern. Examples of these would be family ties and close friends. Secondary social groups, on the other hand, such as political parties and trade unions, are usually impersonal and instrumental and are formed to fulfill special interests. The recent major sociological themes in research on relationships include the structural changes of relations, inequality and dynamics in relationships, variations over the life course, diversity of relationships, and the connections between individual ties and social context.