What is the role of consciousness in our mental lives? This book argues that consciousness plays an essential role in explaining how we can acquire knowledge and epistemically justified belief about ourselves and our surroundings. On this view, our mental lives cannot be preserved in unconscious creaturesβzombiesβwho behave just as we do. Only conscious creatures have epistemic justification to form beliefs about the world. Zombies cannot know anything about the world, since they have no epistemic justification to believe anything. On this view, all epistemic justification depends ultimately on consciousness. This book builds a sustained argument for the epistemic role of phenomenal consciousness, which draws on a range of considerations in epistemology and the philosophy of mind. The book is divided into two parts, which approach the theory of epistemic justification from opposite directions. Part I argues from the bottom up by drawing on considerations in the philosophy of mind about the role of consciousness in mental representation, perception, cognition, and introspection. Part II argues from the top down by arguing from general principles in epistemology about the nature of epistemic justification. These mutually reinforcing arguments form the basis for a unified theory of the epistemic role of phenomenal consciousness, one that bridges the gap between epistemology and the philosophy of mind.