This book has a relatively long history. It is based on my DPhil thesis, which I completed at Oxford in 2016. For the most part, the claims that are advanced and defended in this book are the same as those that I argued for in the thesis. The thesis that I submitted is not the thesis I originally intended to write. Initially, the aim was to individuate the various types of proprietary interest that English law recognises in respect of chattels. It soon became clear, however, that there are competing conceptions of ‘possessory title’, and that adopting one conception rather than another has important implications for the status of ownership in English law and the limits of relativity of title. It was obvious that one could not adequately engage with these matters in a single chapter. So, the aim of individuating various kinds of proprietary interest was replaced with the aim of understanding the nature of the ‘title’ that is acquired through possession. This is the central objective of this book.