In order for slavery to develop in the British empire, it needed a legal basis. This lecture explores how that legal basis was created in the face of parliament’s refusal, in the 1660s and 1670s, to pass a slave code for the empire. With the support of Charles II and James II, high court judges in England created the legal foundation for considering people as property, crafting a common law foundation for slavery across the empire, one that had immediate impact in the expansion and financing of slavery. When those high court decisions began to be challenged in England itself during the eighteenth century, parliament stepped in to reinforce them for the empire. These decisions laid the basis for legal and financial claims for property in people that anchored slavery in all American states where it continued to be legal in the nineteenth century. But from the very beginning some argued that no one can have property in another. This lecture therefore provides two centuries of debate on the question of property in people that preceded both Dred Scot (1857) and the Civil War. In doing so it traces how arguments about who was a subject versus who was an alien (and what rights aliens have) contributed to the development of American slavery.