By some estimates, in less than two years more people will connect to the Web using a mobile device than traditional fixed broadband. Immediate worldwide digital distribution with a built-in payment system means enormous opportunity for content creators, aggregators, filters, curators, retailers, and of course readers. But the challenges loom large: competition from nimble startups who needn't carry the costs of legacy businesses; uncertain and untested business models; the need to stand out not just among other books on a shelf, but amid the growing universe of rich digital multimedia content billions of people around the world will soon carry with them all the time.