Every day, veterinarians make difficult decisions about their patients, such as ‘What treatment is best?’ or ‘Which diagnostic test should I use?’ In veterinary medicine, there are many sources of evidence to inform clinical decisions, including peer-reviewed primary research studies (such as those published in peer-reviewed journals such as the Journal of the American Veterinary Medical Association), narrative reviews (such as those published in the British journal ‘In Practice’ or the American journal ‘Clinicians Brief’), didactic information given in textbooks, and expert opinion sought and shared (such as on the Veterinary Information Network). These different types of evidence vary in quality, quantity and accessibility; some are more reliable than others. While clinical decisions should be based on the best evidence available, it is sometimes hard to find. Systematic reviews are a form of research - they bring together what is known from the research literature using explicit and accountable methods. The term ‘systematic’ distinguishes them from reviews undertaken without clear and accountable methods. The breadth, depth, and extent of the work done by a reviewer in engaging with a research issue brings a third dimension to the review. It is important for those writing articles or using reviews to know how to summarize the literature and mitigate bias in those summaries. This Masterclass explains what a literature review is and shows the methodologies, terminologies, and biases of performing one.