At the beginning of the 2nd decade of the 21st century, the amount of information available to health care practitioners is immense. Medical websites and journals send daily messages announcing results of the latest studies. Within minutes, subspecialty data heretofore found only in university libraries can be unearthed, along with a vast array of information from academics, commercial organizations, advocacy groups, the government, and seemingly anyone with a computer and an internet connection.

What is the role of a general reference work such as The Merck Manual when seemingly the entire body of medical knowledge is at one's fingertips electronically? With such a vast body of knowledge available, finding a good starting place can be difficult. The Manual has always been intended as the first stop on the road to understanding for readers encountering a topic for the first time or for the first time in a long time. After digesting a Merck Manual topic, readers will be well prepared to understand and evaluate the wealth of more detailed information available elsewhere.

As it has for over 110 years, The Merck Manual focuses on discussions of specific disorders, organized by organ system or medical specialty. In its structured introductions to medical disorders, The Manual provides health care practitioners and students with straightforward, practical explanations of "what to do" to diagnose and treat those conditions. We discuss when to suspect a disease, the proper sequence of evaluation, and the first-line options for treatment along with selected alternatives. In addition, we provide enough background information on etiology and pathophysiology to ensure comprehension of the management recommendations.

The Manual continues to enhance its accessibility. In addition to having introductory "nutshells" at the beginning of each disease discussion, we have included bulleted lists in the text whenever possible, including at the beginning of diagnosis and treatment discussions.

In the interest of brevity, The Merck Manual has never cited references to the medical literature. Nonetheless, readers can be assured that our hundreds of contributors and dozens of peer reviewers are presenting the best current recommendations, soundly based on available evidence.

Although the printed Merck Manual has long since grown too big to be carried in a lab coat, it has returned to the pocket as content on many different handheld electronic devices. In addition, The Merck Manual continues to be available to all readers free of charge at www.themerckmanual.com. Although our electronic versions have a currency that a printed product cannot, the book still provides a better in-depth reading experience along with a tactile satisfaction and ease of perusal not possessed by electronic devices. Undoubtedly this will change as technology advances, but whatever the platform, we will continue to strive to keep The Merck Manual as useful as ever.

We thank the numerous contributors who have worked diligently with us to craft this edition, and we hope you will find it worthy of continued and frequent use. As always, suggestions for improvements will be warmly welcomed and carefully considered.

Robert S. Porter, MD, Editor-in-Chief

Last full review/revision February 2010

Content last modified February 2012