Peer review and assessment are vital elements in numerous scientific decisions, particularly scientific publishing, research funding and regulatory science. This handbook provides an essential reference for all those involved in these processes, including reviewers, reviewees and review managers. It guides the reader though all of the important aspects of peer review and explains how they are applied in the design and operation of successful review and assessment programs. Key topics include the selection of reviewers, identifying and mitigating conflicts of interest and developing review criteria. The more general question of how scientific claims can be evaluated and controversies resolved is also considered in an exploration of the Best Available Science concept. A large appendix supplements the main chapters and provides further useful information on related topics such as manuscript management, stakeholder participation and quality assurance.