Systematic review (SR) focuses on a specific question and aims to answer it. For example, a SR may be used to estimate the efficacy of an intervention or impact of an exposure. SR uses standardised, systematic methodology to search for evidence (published and unpublished literature from multiple sources) and collate, critically appraise and synthesise it to answer the review question. This methodology aims to be transparent and reduce bias. Studies included may be presented in a searchable systematic map database. Implications for research, policy and practice are provided. Click here for an example of a SR carried out by the CEBA. Guidelines for SR can be found on the Collaboration for Environmental Evidence website.