This volume focuses on Berkeley’s doctrine of signs. The ‘doctrine of signs’ refers to the use that Berkeley makes of a phenomenon that is central to a great deal of everyday discourse: one whereby certain perceivable entities are made to stand in for (as ‘signs’ of) something else. Things signified might be other perceivable entities or they might also be unperceivable notions – such as the meanings of words. From his earliest published work, A New Theory of Vision in 1710, to those works written towards the end of life, including Alciphron in 1732, Berkeley is at pains to emphasise the crucial role that sign-usage, particularly (but not only) in language, plays in human life. Berkeley also connects sign-usage to our (human) relationship with God: an issue that was right of the heart of his philosophical project. The contributions in this volume explore the myriad ways that Berkeley built on such insights to better understand a range of philosophical issues – issues of epistemology, language, perception, mental representation, mathematics, science, and theology. The aim of this volume is to establish that the doctrine of signs can be seen as one of the unifying themes of Berkeley’s philosophy. What’s more, this theme is one which spans his whole philosophical corpus; not just his best-known works like the Principles and the Three Dialogues, but also his works on science, mathematics, and theology.