Clinical practice guidelines have been developed to improve the process and outcomes of health care and to optimize resource utilization. By addressing such issues as prevention, diagnosis, and treatment, they can aid in health care decision making at many levels. Several other decision aids are cast in the guideline lexicon, regardless of their focus, formulation, or format; this can foster misunderstanding of the term "guideline." Whether created or adapted locally or nationally, most guidelines are an amalgam of clinical experience, expert opinion, and research evidence. Approaches to practice guideline development vary widely. Given the resources required to identify all relevant primary studies, many guidelines rely on systematic reviews that were either previously published or created de novo by guideline developers. Systematic reviews can aid in guideline development because they involve searching for, selecting, critically appraising, and summarizing the results of primary research. The more rigorous the review methods used and the higher the quality of the primary research that is synthesized, the more evidence-based the practice guideline is likely to be. Summaries of relevant research incorporated into guideline documents can help to keep practitioners up to date with the literature. Systematic reviews have also been published on the dissemination and implementation strategies most likely to change clinician behavior and improve patient outcomes. These can be useful in more effectively translating research evidence into practice.