International Classification of Diseases: The CDC has excellent pages that describe and explain the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) and International Classification of Diseases,Ninth Revision, Clinical Modification (ICD-9-CM). Each site includes all the smaller individual revisions to each larger revision and links to the codes themselves.
National Guideline Clearinghouse
NGC was created by Agency for Healthcare Research and Quality (AHRQ) in partnership with the American Medical Association and the American Association of Health Plans (now America’s Health Insurance Plans [AHIP]). Its mission is to provide health professionals, health care providers, health plans, integrated delivery systems, purchasers, and others an accessible mechanism for obtaining objective, detailed information on clinical practice guidelines and to further their dissemination, implementation, and use.