In social psychology, similarity refers to how closely attitudes, values, interests and personality match between people. Despite sayings about opposites attracting, research has consistently shown that similarity leads to interpersonal attraction.

Many forms of similarity have been shown to increase liking. Similarities in opinions, interpersonal styles, amount of communication skill, demographics, and values have all been shown in experiments to increase liking.

Several explanations have been offered to explain similarity increases interpersonal attraction. First, people with similar interests tend to put themselves into similar types of settings. For example, two people interested in literature are likely to run into each other in the library and form a relationship (involving the propinquity effect). Another explanation is that we notice similar people, expect them to like us, and initiate relationships. Also, having relationships with similar people helps to validate the values held in common. Finally, people tend to make negative assumptions about those who disagree with them on fundamental issues, and hence feel repulsion.

See also: Rapport