U.S. Sen. Scott Brown, a Republican, a Democrat.
Warren will take office as the state's junior senator in January.
She'll replace Brown, who was elected in a special election in January 2010 when he defeated Democrat Martha Coakley.
In his concession speech on Tuesday night, Brown told supporters that "defeat is only temporary."
As soon as the race was called, analysts began suggesting Brown may run for Massachusetts governor in 2014 or would seek the state's other U.S. Senate seat if Sen. John Kerry is named Secretary of State under President Barack Obama in his second term.
What should Brown do next? Tell us in the comments.