A pressing problem often facing commercial practitioners is how to determine the principle which would dictate when a proprietary claim is available and when it is not. This book explains the nature and structure of key interests in property in commercial transactions and analyses the incidence of proprietary claims available to holders of different interests in assets. It starts by identifying the structure of those interests which the author terms ‘lesser proprietary interests’, comprising security interests and interests based on retention of title in contracts of sale of goods, hire-purchase agreements, and leases, thereby contributing to the understanding of concepts which are traditionally used to explain this area of law such as bailment and fiduciary relationship. The book examines the circumstances in which the interests are lost and the extent to which proprietary claims can be asserted in assets that derive from the original subject matter, that is proceeds, products and income, as well as in accretions. It examines these claims at three levels: as a matter of default rules in the absence of misappropriation of the original subject matter; as a matter of contract; and in circumstances in which the original subject matter has been misappropriated. The book approaches the topic of tracing and derived assets in commercial transactions on a principled basis.