The Contemporaries: Travels in the 21st-Century Art World

It's been nearly a century since Marcel Duchamp exhibited a urinal and called it art. Since then, painting has been declared dead several times over, and contemporary art has now expanded to include just about any object, action, or event: dance routines, slideshows, functional hair salons, seemingly random accretions of waste. In the meantime, being an artist has gone from a join-the-circus fantasy to a plausible vocation for scores of young people in America.

But why--and how and by whom-...