How long?

So what keeps the Stones going? Money, yes. But the band could make big bucks simply by doing commercials instead of touring. Going on the road is about ego gratification. "This whole thing runs on passion," says Richards. "Even though we don't talk about it much ourselves, it's almost a sort of quest or mission."

The Stones and their estates will continue licensing songs and selling records for years. But sooner rather than later, the touring will cease. Jagger's stage antics are remarkable when you consider his age. But how much longer? Charlie Watts, the oldest Stone, is already 61. The band hasn't said this is the last tour, though it could be--and of course that kind of speculation is great for ticket sales, particularly in second-tier cities, where this really could be the Stones' last show.

"How long can we go on?" asks Keith. "Forever. We'll let you know when we keel over." And when that day comes, it will mean not only the end of the world's greatest rock band but also a winding-down of one of the most successful enterprises this crazy business has ever known.