The point is not to retire from work," Hoover warned, "or you will shrivel up into a nuisance to all mankind." More than most of us, ex-presidents can afford to spend all their time relaxing. But they don't. Even as they downshift, they look for ways to use their talent and influence. Truman counted on Hoover — his personal and political opposite — to organize a massive famine-relief program in Europe in the immediate aftermath of World War II, before the launch of the Marshall Plan. The ability to serve such a cause, Hoover told friends, added 10 years to his life.

Perhaps no former president has shown the redemptive and rehabilitative power of a well-played second act as much as Jimmy Carter. "There are two periods in our lives when we have exceptional freedom: at college age and when we begin our retirement years," Carter said. "Retirement years are a time to define, or redefine, a successful life." For him this meant writing books. The first, Everything to Gain: Making the Most of the Rest of Your Life (written with wife, Rosalynn), was very difficult, because part of the research involved rereading 6,000 pages of diary notes he dictated during his presidency — the good days and the bad. But he stuck with it and has now produced a total of 25 titles, including poetry, prayer and children's books. He rediscovered woodworking, took up oil painting and learned Spanish. And as Carter reinvented himself, he reinvented the post-presidency, becoming so effective a global activist promoting democracy and fighting disease that he won the Nobel Peace Prize, in 2002.

Others have taken a more private path. George W. Bush spends time painting portraits of dogs, and he works with veterans on physical rehabilitation through mountain biking. "I have no desire for fame and power anymore," he says.

When you're part of a couple, retirement is a two-person job, and recent Oval Office occupants seem to recognize that. Jimmy and Rosalynn Carter have been married 66 years. Their secret? "We give each other space," Rosalynn once told a reporter. "That's really important. It was most important after we came home from the White House, because we'd never been at home all day together every day." Nixon urged Carter to be sure and get his wife an office when he left Washington; Rosalynn, Nixon wisely noted, had her own transition to make. When Lyndon and Lady Bird Johnson arrived home at their ranch to find their luggage piled in a mound in the carport and no aides racing to carry the bags in, Lady Bird started to laugh. "The coach has turned back into a pumpkin," she said. "And the mice have all run away."

Next: Life after the White House for former first ladies. »