Several methods can be used to identify systematic reviews. These include bibliographic databases, such as MEDLINE, Best Evidence, and the Cochrane Library. In the future, the Cochrane Library could become the source of choice for systematic reviews because it provides the full text for Cochrane reviews and citations to many other systematic reviews. Moreover, the Library is growing rapidly and becoming more readily available, and its searching capabilities are being improved with each update. Although Best Evidence contains fewer systematic reviews than the Cochrane Library, it is specifically designed for practicing internists and primary care physicians and includes systematic reviews on diagnosis, cause, prognosis, and quality improvement. At present, however, MEDLINE and other bibliographic databases are probably the most up-to-date and readily available sources of systematic reviews. Systematic reviews are a powerful and useful way to assemble evidence; however, just because a review has been done using systematic review methods does not guarantee that its results are credible. Regardless of the source, all systematic reviews (like all types of research evidence) require critical appraisal to determine their validity and to establish whether and how they will be useful in practice.