Systematic reviews bring together individual research studies that investigate the same clinical or research question and summarize the available evidence. They are called "systematic" reviews because they follow explicit methods for finding, analyzing, and summarizing the research. These explicit methods help reduce bias and ensure that the methodology can lead to reproducible results. Because of this explicit, rigorous process, systematic reviews are considered the "gold standard" for evidence-based practice.

Systematic reviews are considered secondary (or filtered) sources because the reviewers are synthesizing and summarizing research done by other people. The individual studies included in a systematic review are considered primary (unfiltered) sources because they represent original research. These individual studies are often randomized controlled trials.