IF you were one of the few brave readers of printed books in 2007 who crossed the divide into digital reading, your options were sparse and expensive. The original Amazon Kindle, for example, cost $400, and its screen displayed a mere four shades of gray.

Today, digital readers are much cheaper and come with significantly better displays and storage space. But things are just getting started  like the price war that erupted last week between Amazon and Barnes & Noble that pushed the prices of their e-books below $200. Those e-readers are also facing challenges from other gadgets that can display books, newspapers and magazines, including mobile phones and the new tablet computers like the iPad. Apple said last week that it had sold 3 million iPads in 80 days.

“The paper book is dead,” says the digital visionary Nicholas Negroponte.

So what’s next for these digital book replacements? Will the e-reader be reduced to a tiny chip that can be implanted in our retina by 2015? Not quite, but those who think a lot about the future say e-readers are set to take on new shapes and sizes, and their prices will continue to fall.

Mr. Negroponte runs a nonprofit group that hopes to put inexpensive computers in the hands of millions of impoverished children around the globe. Its efforts helped push the commercial development of the popular netbook, the cheap small laptop computers that have grown in popularity in the last few years. He agreed that the price of e-readers eventually will fall to $50 and perhaps even $20.