We shall begin our discussion of the history of the problem of personal identity with John Locke, who gives the problem its first clearly identifiable formulation in the famous chapter ‘Of identity and diversity’ in his Essay Concerning Human Understanding (1961, Book II, Ch. 27). It has been said that all subsequent philosophy consists merely of footnotes to Plato. On this topic, at least, it can be truly said that all subsequent writing has consisted merely of footnotes to Locke. Indeed, many present-day philosophers writing on personal identity would still be happy to describe themselves as ‘Lockean’ or, at least, ‘neo-Lockean’ in their approach to the topic, whilst many others would naturally define their positions by their opposition to Locke. Locke’s discussion of personal identity is thus far from being of merely historical interest to us.