The internalism-externalism debate is one of the oldest debates in epistemology. Internalists assert that the justification of our beliefs can only depend on facts internal to us, while externalists insist that justification can depend on additional, for example environmental, factors. In this book Clayton Littlejohn proposes and defends a new strategy for resolving this debate. Focussing on the connections between practical and theoretical reason, he explores the question of whether the priority of the good to the right (in ethics) might be used to defend an epistemological version of consequentialism, and proceeds to formulate a new 'deontological externalist' view. His discussion is rich with insights and will be valuable for a wide range of readers in epistemology, ethics and practical reason.