Within psychology, most aspects of ownership have received scant attention or have been overlooked completely. In this chapter, the authors outline 21 reasons why it will be important (and interesting) to understand the psychological basis of ownership of property, including its developmental origins: (1) Daily life; (2) A human universal, and cultural and cross-species variation; (3) Myriad inferences; (4) An abstract concept; (5) Object cognition; (6) Beyond objects; (7) Behaving in relation to things; (8) Social behavior; (9) Understanding behavior; (10) Rights and transgressions; (11) Responsibilities of owners; (12) Social relationships; (13) Distributive justice and moral development; (14) Socialization; (15) Social recognition; (16) Conflicts; (17) First- versus third-person perspectives; (18) The self and self-image; (19) Psychology and law; (20) Mental illness and crime; and (21) A meeting of domains.