Abstract The Prologue provides historical perspective and motivation for the book, as well as a preview of its contents. We note the recurring philosophical conflict between ‘perception’ and ‘reality’ down the ages, drawing historical parallels with the Copernican revolution in astronomy and with the rise of atomic theory in thermodynamics. We explain why reality inevitably wins out over perception, despite the perennial scepticism. We show how the notoriously confused theory of quantum physics can be clarified by admitting a reality behind the scenes, that lies beyond our present perceptions. The Prologue ends with an outline of pilot-wave theory and of the main conclusions of the book.