This document provides an introduction to systematic literature reviews. It defines what a systematic literature review is, differentiates it from traditional reviews, and outlines the key stages in conducting an SLR. A SLR uses a systematic and comprehensive approach to minimize bias by documenting an a priori protocol. The stages discussed are formulating the research question, carrying out searches, selecting studies, extracting data, assessing risk of bias, synthesizing evidence, and defining the protocol. History and rationale for using SLRs to summarize research evidence rigorously are also presented.