This study concerned the relationship between views of possession and theft. Four groups of children aged 7-8; 9-10; 12-13 and 16-17 completed a questionnaire based on the work of Furby (1980 a and b) and Irving and Siegal (1983). Results demonstrated that possession concepts become more differentiated with age, focusing more on the importance of positive acquisition, single ownership and social influence. Attitudes towards theft crimes become more harsh even in the face of mitigating circumstances. This increased harshness may be understood in terms of possessions becoming progressively more a part of the self-concept. Thus theft and consequent loss to self leads to empathy with the victim and feelings of retribution for the thief. The results are discussed in terms of the literature on social and moral development.