Robert Metcalfe (born 1946 in Brooklyn, New York) is an American technology pioneer who invented Ethernet, founded 3Com and formulated Metcalfe's Law.

Bob Metcalfe was working at Xerox PARC in 1973 when he invented Ethernet, a standard for connecting computers together over short distances. In 1979, Metcalfe departed PARC and founded 3Com, a manufacturer of computer networking equipment.

In 1980, he was the recipient of the Association for Computing Machinery Grace Murray Hopper Award for his work in the development of local networks, specifically the Ethernet.

In 1990, Metcalfe retired from 3Com and was for 10 years a publisher and pundit writing an Internet column for InfoWorld. He became a venture capitalist in 2001 and is a General Partner at Polaris Venture Partners .

He graduated from MIT with two Bachelor's degrees, one in electrical engineering and another in industrial management from MIT's Sloan School of Management. He earned his Ph.D. from Harvard University, with a thesis on packet switching (which was actually written while working at MIT's Project MAC).

Metcalfe received the National Medal of Technology from President Bush in a White House ceremony on March 14, 2005, "for leadership in the invention, standardization, and commercialization of Ethernet." In 2004, according to IDC, there were 200 million new Ethernet ports shipped worldwide.