It is a standard feature of modern philosophy, at least from Locke, to tie together the questions of how we perceive the world and what we have reason to think the world is like in itself. This is a natural connection, because the questions of how we perceive it, and what kind of conception of it we can best form on the basis of that mode of perception, are obviously intimately linked. Part I of this volume defends the sense-datum theory of perception against its opponents, and argues that the sense-datum theory is much closer to a form of direct realism than is normally thought: we directly perceive the world in the form that it naturally manifests itself to creatures like us. This leaves open the question of what it is like in itself, and Part II tries to show that a Berkeleian interpretation-that the world is a nomological structure in the mind of God-is the most plausible option. Arguments with roots in Berkeley, in modern philosophers such as John Foster, and in modern science, are drawn on to support this conclusion.