Traditional review articles provide clinicians with syntheses of the medical literature but are criticised as being haphazard in their methodology and biased in their conclusions. Systematic reviews use rigorous methods to minimise bias and statistical methods to synthesise results (meta-analysis) that increase power and precision. They permit investigation of generalisability and consistency, improve transparency of methodology, and enhance reproducibility. This article examines the science of systematic reviews and meta-analysis and their relevance to clinical psychiatry. It evaluates the potential errors and sources of bias of meta-analysis, and offers guidelines for evaluation of systematic reviews. It highlights the efforts of the Cochrane Collaboration which is an international organisation involved in preparing, maintaining and disseminating highly structured, frequently updated, and good quality systematic reviews of the effects of interventions in all aspects of health care.