A major reason the Internet has been such a boon to business is that it's been a single network, accessible to anyone from anywhere. Any entrepreneur can create a website that can be accessed by literally hundreds of millions of users. What country a customer lives in or what Web service he or she uses may affect how fast a website loads, but we're all connected to the same Internet. Unfortunately, that is changing rapidly.

The principal of maintaining the Internet as a single, interconnected network with no preference for one type of bits over another--what geeks call "network neutrality"--is under assault. Foreign countries have led the charge. Saudi Arabia blocks content that runs counter to the clerics' interpretation of Islam. China bars its citizens' access to sites created by, among others, practitioners of Falun Gong. What results is the fragmentation of the Internet. The network that we've grown accustomed to over the past decade is, in a very real sense, becoming multiple Internets, because the Internet you encounter from within China is different from the Internet you encounter in the United States.

Western companies have helped accelerate this process by manufacturing the routers and software designed to let foreign governments filter the Internet. Prominent Internet companies based in the U.S. have also signaled that they are willing to work in a world where there are Internets rather than a single Internet. Because Google is routinely blocked by the Chinese firewall, for example, it has created a truncated index called Google.cn for its Chinese customers. The search giant has decided that providing at least some service in China--and disclosing to the rest of the world which searches are censored--is better than simply opting out of the Chinese Internet.

It's not just repressive regimes that are trying to turn the Internet into the Internets. Customers of the Canadian cable company Shaw will find that Vonage runs slowly on that network. In fact, Shaw warns users of all VoIP services that they may experience connection issues unless they pay a $10-per-month enhancement fee. It shouldn't surprise you to know that Shaw offers a competing digital service. Similarly, phone carriers in Africa cut service to local Internet service providers when it became clear that those ISPs were enabling VoIP calls, reducing demand for the carriers' lucrative long-distance services.

The next frontier in the battle over network neutrality is likely to be the delivery of video services. BellSouth and AT&T have announced plans to sell "premium" network services that deliver video from some providers more quickly than video from others. If, say, a company like Yahoo pays AT&T a fee, its videos will download faster and at a higher quality than videos downloaded from Google, should Google choose not to pay. Google might be able to play this game, but the average business will not be able to. Premium services create a barrier to innovation in what has been one of humanity's most innovative spaces.

What may happen to companies in this brave new world? Soon, it no longer may be sufficient to know that you're connected to "the Internet"--businesses will need to know where the bits they want are, and whether the provider they're using for Internet service considers them premium or substandard. It will no longer be possible for a start-up to put a site on the Internet and assume that it's equally accessible to everyone in the world. And existing companies may suddenly discover that they are reaching much smaller audiences than they've grown used to. The fragmentation of the Internet is the fragmentation of markets.

In the same way that Chinese Internet users have gotten used to the fact that they're connected to a network that delivers some bits quickly and some not at all, American users will discover the costs of a nonneutral network. Before AT&T and BellSouth move ahead with their plans to create premium services, they must win congressional approval. American entrepreneurs and consumers, and the politicians who represent them, may want to think very carefully before they embrace a world of many Internets.

Ethan Zuckerman is a research fellow at the Berkman Center for Internet & Society at Harvard Law School and co-founder of weblog community Global Voices.