A theory of friendship is proposed which emphasizes the importance of the interaction process to the participants' choice of friends. It is suggested that persons will prefer for friends those with whom they have experienced encounters which are validating, successful and effective. Validation is defined as the correspondence between the actor's self-image and the impression of others; success is defined as the favorableness of the other's responses; and effectiveness is defined as the correspondence between the self actor intended to project and the other's impression. The major implication of the theory is tested in the small group setting and the results indicate the empirical validity of the theoretical propositions.