- Harrison's Principles of Internal Medicine is considered the most reliable textbook in medicine. The 18th edition has been extensively modified and expanded by leading doctors. - It covers more aspects of global medicine than any other textbook, including new sections on systems biology, the human microbiome, biology of aging, and neuropsychiatric disorders in war veterans. - In addition to comprehensive coverage of disease systems and management, it includes a multimedia DVD with over 2,000 images and videos demonstrating clinical procedures, as well as PowerPoint presentations for classroom lectures.