Republican presidential candidate Mitt Romney has selected Wisconsin Rep. Paul Ryan to be his running mate.

The candidate made his announcement to supporters via a phone app, saying

"Mitt's Choice for VP is Paul Ryan."

Romney and Ryan are kicking off a four-day bus tour that will take them to as many states.

Romney says Ryan is a man of what he calls "great steadiness" and "unquestioned integrity." The former Massachusetts governor says Ryan is a "shining exception" in a political world of pettiness.

The two appeared together for the first time as the Republican presidential ticket on Saturday morning in Virginia. They faced supporters while standing on the USS Wisconsin, a retired aircraft carrier.

Just hours after his campaign confirmed Ryan as his selection, Romney says Ryan won't demonize his opponents. Romney says that Democrats may disagree with Ryan's policies, but he doesn't know anyone who doesn't respect his character and judgment.

At 42, Ryan is a generation younger than the 65-year-old Romney.

See the announcement here.