Merck & Co., Inc. ( ), also known as Merck Sharp & Dohme or MSD outside the USA and Canada, is one of the largest pharmaceutical companies in the world. The headquarters of the company is located in Whitehouse Station, NJ. It was established in 1891 as the United States subsidiary of the German company now known as Merck KGaA. In common with many other German assets in the United States, Merck & Co. was confiscated in 1917 during World War I and set up as an independent company. It is currently one of the seven largest pharmaceutical companies in the world both by capital and revenue.

Merck & Co. or MSD describes itself as a “a global research-driven pharmaceutical company. Merck discovers, develops, manufactures and markets a broad range of innovative products to improve human and animal health, directly and through its joint ventures.” The Merck Company Foundation has distributed over $480 million to educational and non-profit organizations since it was founded in 1957.

Merck publishes the Merck Manual of Diagnosis and Therapy, the world's best-selling medical textbook, and the Merck Index, a collection of information about chemical compounds.