This chapter on critical appraisal provides an essential guide to students and researchers on the what, why and how of an increasingly important set of skills in health research. Indeed, critical appraisal is now a key tenet of academic writing and scholarship. This chapter covers: what critical appraisal is; why critical appraisal is important; critical appraisal tools and checklists, including an overview of how to find and select them for different research designs; and useful practical guidance on how to assess methodological quality what, why, when and how.