Eisai Co., Ltd. is a Japanese pharmaceutical company focused on developing and commercializing treatments primarily in neurology, oncology, and other therapeutic areas, including gastrointestinal and metabolic diseases. Established in 1941 and headquartered in Tokyo, Eisai has grown into a global presence, with research, development, and commercial operations across North America, Europe, and Asia. The company’s mission centers on "human health care" (hhc), prioritizing patient needs and well-being.

Eisai is especially recognized for its advancements in Alzheimer's disease treatments, collaborating with companies like Biogen to develop drugs targeting neurodegenerative diseases. Beyond pharmaceuticals, Eisai invests in diagnostics, digital health solutions, and partnerships that support innovative healthcare approaches, especially in underserved therapeutic areas.