Mark Sundeen, Riverhead, 260 pages, $15

In 2000, when Daniel Suelo was 39, he put his last $30 inside a phone booth and walked away. He has not used money since. Author Mark Sundeen, who has written an extraordinary and thought-provoking book about this strange man, assures readers that Suelo "came from a good family and had been to college. He was not mentally ill, nor an addict. His decision appears to have been an act of free will by a competent adult."

It would have been amazing enough if he had lived without money for one year, as an exercise. Extraordinary if he did it for two, or five. But for 12 years? With no signs of stopping yet?

"I know it is possible to live with zero money," he says. "Abundantly."

He sleeps in caves in the Utah canyonlands much of the time, although he also house-sits. He accepts meals from friends, but also goes dumpster-diving in search of discarded food that is still edible. He occasionally works, but not for money.

He's been accused of being a mooch and a freeloader, but he doesn't see it that way. He accepts what is freely given -- or what is discarded, in the case of picking clothes out of the trash -- and he gives freely in return. So although there's no money involved, there is nevertheless an odd sort of currency in his life.

Believing that things will somehow show up when he most needs them -- and, oddly enough, they often do -- he has relinquished control to chance. He says, and seems to really believe, that "everything happens for a reason."

Sundeen meets with Brian Mahan, who once taught Suelo at the University of Colorado and is an expert on the tension between worldly success and spiritual meaning. The professor says that he "never envisioned anyone being quite that radical." But he sees Suelo's quest as "a deeply moral act."

And rather than challenging Suelo, he says, "it is for all of us to answer why we question the Dans in the world."