In certain circumstances the law has seen competing claims made to goods by persons who do not own them and who have come into possession of them without the consent or knowledge of the owner of them. Such claims may be made, typically, where goods which have been lost by their owner are found by someone who takes possession of them; or where goods have been stolen and are in the possession of the thief or a person who has received or taken them from the thief. In such cases, of course, the proprietary title of the owner remains paramount but, in the absence of an owner to assert such a claim, the question of entitlement to found or stolen goods may be disputed by other parties who have taken possession of the goods, dealt with them in some way or had some relation to them. In such disputes, legal proceedings, usually in conversion, may be undertaken by the plaintiff with the purpose of establishing an interest in the goods sufficient to prevail over any claimed interest of the defendant.1 The purpose of this paper is to discuss the interests involved in cases of found and stolen goods, and to describe the way in which the law deals with rival claims in such cases. The nature of the possessory right necessary to found a successful conversion action in the absence of the true owner of goods is central to such a discussion, and an attempt will be made to analyse the principles involved in this context in establishing such a right. In particular, this paper revisits and questions the correctness of the reasoning in Costello v Chief Constable of Derbyshire,2 which equated the interests of finders, thieves and other wrongdoers; and concludes that the decision failed to make the necessary distinction between the respective rights in goods of finders, thieves and others who are in possession of unlawfully obtained goods.