Friendship is a form of interpersonal relationship generally considered to be closer than association, although there is a range of degrees of intimacy in both friendships and associations. Friendship and association can be thought of as spanning across the same continuum. 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:

    The tendency to desire what is best for the other
    Sympathy and empathy
    Honesty, perhaps in situations where it may be difficult for others to speak the truth, especially in terms of pointing out the perceived faults of one's counterpart
    Mutual understanding and compassion
    Trust in one another (able to express feelings - including in relation to the other's actions - without the fear of being judged); able to go to each other for emotional support
    Positive reciprocity - a relationship is based on equal give and take between the two parties.