This site is intended only for residents of the United States and its territories. Visit MerckManuals.com for the latest medical information. First published in 1899 as a small reference book for physicians and pharmacists, The Merck Manual grew in size and scope to become one of the world's most widely used comprehensive medical resources for professionals and consumers. As The Manual evolved, it continually expanded the reach and depth of its offerings to reflect the mission of providing the best medical information to a wide cross-section of users, including medical professionals and students, veterinarians and veterinary students, and consumers. For access to thousands of medical topics with images, videos and a constantly expanding set of resources, visit MerckManuals.com.