Lewis McAdory Branscomb (August 17, 1926 – May 31, 2023) was an American physicist, government policy advisor, and corporate research manager.

He was best known for being head of the National Bureau of Standards and, later, chief scientist of IBM; and as a prolific writer on science policy issues.

These years, and his interactions with scholars as diverse as Clyde Kluckhohn, Merle Fainsod, William Fairbank, and Edward Purcell, kindled a lifelong interest in broad policy issues.

Rising in management through several levels, he became the founding chair of the Joint Institute for Laboratory Astrophysics (JILA), and was in 1969 appointed director of the National Bureau of Standards by President Nixon.

In 1998, Branscomb was awarded the Okawa Prize "for outstanding contributions to the progress of informatics, scientific and technological policy and corporate management."