Friendship is a relationship between friends, a friendly feeling or attitude. Friends care for one another and look out for each other. For a deep understanding to occur between friends, they must open up about personal things, listen carefully, and be loyal to one another (Kheterpal, 2008) Friendships and associations are often thought of as spanning across the same continuum and are sometimes viewed as weaknesses. The study of friendship is included in the fields of sociology, social psychology, anthropology, philosophy, and zoology. Various academic theories of friendship have been proposed, among which are social exchange theory, equity theory, relational dialectics, and attachment styles.

Value that is found in friendships is often the result of a friend demonstrating the following on a consistent basis:

This article covers many different aspects of friendship including the definition, cultural variations including the decline of friendship in the U.S., friendship across life stages, and different types of friendship.