GMAC or G-MAC may refer to:
Organizations Ally Financial (General Motors Acceptance Corporation), traded as GMAC until 2010 GMAC Insurance, former name of National General Insurance GMAC Real Estate, a former real estate franchised brokerage firm GMAC ResCap (Residential Capital), which includes GMAC Mortgage GMAC Re, a former reinsurance company of GMAC Graduate Management Admission Council, an international association of business schools GMA Canada, the Gospel Music Association of Canada, formerly the CGMA Global Markets Advisory Committee, part of the U.S. Commodity Futures Trading Commission
Computing Galois Message Authentication Code, a type of cryptographic message authentication code Giga multiply–accumulate operations per second, a rate of multiply–accumulate operations Gigabit media access controller, for handling an Ethernet physical transceiver; See Gigabit Ethernet
Other uses Graeme McDowell (born 1979), Northern Irish professional golfer nicknamed G-Mac GMAC Bowl, a sponsored game of college level American football, now known as the LendingTree Bowl Great Midwest Athletic Conference, a U.S. college athletic conference established in 2011 and starting competition in 2012
See also GMAC massacre, a 1990 shooting by James Edward Pough in a car loan office in Florida, US