The foundation of evidence-based medicine is critical analysis and synthesis of the best data available concerning a given health problem. These factual data are accessible because of the availability on the Internet of web tools specialized in research for scientific publications. A bibliographic database is a collection of bibliographic references describing the documents indexed. Such a reference includes at least the title, summary (or abstract), a set of keywords, and the type of publication. To conduct a strategically effective search, it is necessary to formulate the question - clinical, diagnostic, prognostic, or related to treatment or prevention - in a form understandable by the research engine. Moreover, it is necessary to choose the specific database or databases, which may have particular specificity, and to analyze the results rapidly to refine the strategy. The search for information is facilitated by the knowledge of the standardized terms commonly used to describe the desired information. These come from a specific thesaurus devoted to document indexing. The most frequently used is MeSH (Medical Subject Heading). The principal bibliographic database whose references include a set of describers from the MeSH thesaurus is Medical Literature Analysis and Retrieval System Online (Medline), which has in turn become a subpart of a still more vast bibliography called PubMed, which indexes an additional 1.4 million references. Numerous other databases are maintained by national or international entities. These include the Cochrane Library, Embase, and the PASCAL and FRANCIS databases.