Abstract: When companion animal interact closely with people, the roles they play may be categorized in terms of three major functions. The projective function involves the extent to which pets may serve as a symbolic extension of the self. The sociability function involves the role of pets in facilitating human-to-human interaction. The surrogate function involves the extent to which interaction with pets may supplement human-to-human interaction, or serve as a substitute for it. A person publicly identified with a companion animal makes a symbolic statement of their personality and self-image. Whether or not this process is intentional, the presence of a pet and the way it is treated become factors which are taken into account in the assessment of the social self. Pets facilitate interaction by being social lubricants. They provide a neutral subject of conversation, and perform a variety of functions as social catalysts. Since interaction with companion animals can approximate human companionship, the presence of pets may serve to supplement the benefits usually derived from the roles of friend, parent, spouse, or child. Alternatively, pets may serve as surrogate antagonists. In the extreme, interaction with companion animals may not only supplement human companionship, but may actually replace it. These three major functions are discussed with examples. Implications are noted for future research on companion animals.