Clinical epidemiology, a field that tries to establish systematic approaches to gathering and interpreting clinical evidence in the care of patients, has grown considerably over the last few years. Several textbooks appeared with this growth, and one of these books, Clinical Epidemiology: The Essentials, is in its second edition. This introductory textbook, geared toward the practitioner, is organized into chapters by clinical activities such as diagnosis, prognosis, and treatment, and by epidemiologic concepts such as risk, frequency, and cause. With several revisions to the first edition, and new chapters on prevention and meta-analysis, the book remains concise, clearly written, and