Systematic reviews are at the cornerstone of evidence-based medicine and healthcare. They give us the opportunity to combine data in order to improve consistency of results demonstrated in randomised controlled trials, and therefore contribute to clinical decision making. Systematic reviews can be used in many different fields, but the current focus in the health care field is on the evaluation of interventions, as demonstrated by the Cochrane Library. This book provides an introductory explanation of systematic reviews in a health care setting, and covers both intervention and aetiology focussed research questions.