Merck & Co., Inc. operates as a healthcare company worldwide.

It operates through two segments, Pharmaceutical and Animal Health. The Pharmaceutical segment offers human health pharmaceutical products in the areas of oncology, hospital acute care, immunology, neuroscience, virology, cardiovascular, and diabetes, as well as vaccine products, such as preventive pediatric, adolescent, and adult vaccines.

The Animal Health segment discovers, develops, manufactures, and markets veterinary pharmaceuticals, vaccines, and health management solutions and services, as well as digitally connected identification, traceability, and monitoring products.

The company serves drug wholesalers and retailers, hospitals, and government agencies; managed health care providers, such as health maintenance organizations, pharmacy benefit managers, and other institutions; and physicians and physician distributors, veterinarians, and animal producers.

It has collaborations with AstraZeneca PLC; Bayer AG; Eisai Co., Ltd.; Ridgeback Biotherapeutics LP; and Gilead Sciences, Inc. to jointly develop and commercialize long-acting treatments in HIV, as well as a collaboration with Bionomics to identify novel a7 nAChR PAMs suitable for the treatment of cognitive disorder; and clinical trial collaboration and supply agreement with Ankyra Therapeutics to evaluate ANK-101 in combination with KEYTRUDA (pembrolizumab) in patients with advanced solid tumors, as well as a clinical trial collaboration and supply agreement with Phanes Therapeutics, Inc. to evaluate PT886 in combination with KEYTRUDA for the treatment of claudin 18.2 positive gastric or gastroesophageal junction adenocarcinomas, as well as a development and commercialization agreement with Daiichi Sankyo Company, Limited to jointly develop and commercialize Daiichi Sankyo's DXd antibody drug conjugate (ADC) candidates and a collaboration with HiberCell, Inc. Merck & Co., Inc. was founded in 1891 and is headquartered in Rahway, New Jersey.