As of the writing of this article there are 6 different Merck Manuals. The "The Merck Manual of Diagnosis and Therapy" is the world's most widely used medical textbook according to Merck. Other manuals include The Merck Manual of Patient Symptoms," "The Merck Manual--Home Edition" and "The Merck Index." "The Merck Index" is for chemists defining chemicals, drugs and other biologicals.
Anyone can purchase the manuals in book form directly from the Merck website. You can review most of the Merck manuals online, for free. "The Merck Manual of Diagnosis and Therapy," is also available in foreign languages and has an app that you can download to iPods and iPads for easy use. "The Merck Manual of Patient Symptoms" has a podcast that anyone can listen to on various topics.
To use the manual the user must first find the section they seek. The manuals are broken down by topic such as "geriatrics" or "infectious diseases." Under each section is a further listing, in alphabetical order of the items that fall under that topic. Depending on the manual, the definitions may or may not be technical in nature. For example the "The Merck Manual--Home Edition" is written in lay terms, making it easier to understand.
The Merck manuals are not only for people but also for animals. Merck offers two animal-related manuals. "The Merck / Merial Manual for Pet Health" is a resource for pet owners only available in hard copy. "The Merck Veterinary Manual" is a manual used by the veterinary community and offers a similar handbook guide to diseases and treatments found in "The Merck Manual of Diagnosis and Therapy" but for animals instead.