Book excerpt: In an ideal world, our beliefs would satisfy norms of truth and rationality, as well as foster the acquisition, retention, and use of other relevant information. In reality, we have limited cognitive capacities and are subject to motivational biases on an everyday basis. We may also experience impairments in perception, memory, learning, and reasoning in the course of our lives. Such limitations and impairments give rise to distorted memory beliefs, confabulated explanations, and beliefs that are elaborated delusional, motivated delusional, or optimistically biased. In this book, Lisa Bortolotti argues that some irrational beliefs qualify as epistemically innocent, where, in some contexts, the adoption, maintenance, or reporting of the beliefs delivers significant epistemic benefits that could not be easily attained otherwise. Epistemic innocence does not imply that the epistemic benefits of the irrational belief outweigh its epistemic costs, yet it clarifies the relationship between the epistemic and psychological effects of irrational beliefs on agency. It is misleading to assume that epistemic rationality and psychological adaptiveness always go hand-in-hand, but also that there is a straight-forward trade-off between them. Rather, epistemic irrationality can lead to psychological adaptiveness, which in turn can support the attainment of epistemic goals. Recognising the circumstances in which irrational beliefs enhance or restore epistemic performance informs our mutual interactions and enables us to take measures to reduce their irrationality without undermining the conditions for epistemic success.