"Precis: Obstetrics, Fourth Edition", strives to live up to its name by being concise and emphasizing areas of utmost importance to clinical practice. An area of particular importance is obesity. Because obesity is now pandemic, a completely new section that includes the new Institute of Medicine guidelines and information on sleep apnea and bariatric surgery has been added. Another new section is devoted to substance abuse; specifically, the latest information on maternal and fetal effects of illegal drugs, alcohol, and tobacco use. The topic of pain management in pregnancy was refocused from the use of obstetric analgesia and anesthesia to a new section on the management of chronic pain and headache. Other important advances, such as novel, but not yet standardized, screening and treatment modalities for intrauterine growth restriction and the new classification system for intrapartum fetal heart rate monitoring and management are discussed within the contexts of their own sections. Also discussed is appropriate patient education, which is key to optimal patient care. Specific areas calling for patient counseling are identified throughout. Web sites that may be useful to patients and obstetrician - gynecologists seeking additional information are provided in resource boxes throughout. The Editorial Task Force, Advisory Board, and other selected individuals have reviewed the content to ensure that the information is accurate, complete, and current. During this review, an effort was made to ensure consistency with the guidelines of the American College of Obstetricians and Gynecologists as well as to identify emerging areas. As advances unfold, physicians are urged to consult current recommendations.