The days of the internet as a vast, untamed frontier are over, and Eli Pariser wants to make sure you know it.

Pariser is the 30-year-old president of, and with his new book The Filter Bubble: What the Internet Is Hiding from You, Pariser brings a civic-minded skepticism to bear on the increasing "personalization" of the internet.

In the early days of the internet, anonymity was king, conferring the attendant freedom to define yourself as someone other than the crappy loser you were in real life. But the model has shifted: Increasingly, our experience of the web is tied to our actual identities, as we voluntarily blur the boundaries between our "real" lives and our digital ones, via Facebook and other social networking platforms. Meanwhile, companies monitoring our cyber-contrails are hard at work tracking and selling information about who we are.

According to Pariser, personal data company Acxiom has an average of 1,500 pieces of data on each of the people in its database—a database that includes 96 percent of Americans. This information is already used by companies who want to sell you things; increasingly, Pariser argues, it will shape your experience of the internet's content, from the search results you see to the news stories you read to even the spectrum of political discourse you're exposed to.

Facebook provides a clear example of the type of personalization that troubles Pariser: The social networking giant tailors the flow of information in its news feed individually to each user. That's why, even though you have 386 friends, you see updates from the same six people over and over again. This makes a certain amount of sense: The algorithms that generate our news feeds know that of the hundreds of people we collect as friends, some are more relevant than others.

The problem arises, though, when you consider that 36 percent of Americans under 30 get their news through social networking sites. If your news comes through Facebook, and Facebook is filtering which posts you see, the information you end up seeing is highly personalized by the time it reaches you—likely, you're reading posts from people who generally share your ideas and opinions.

Pariser is not alone in seeing personalization as the future of the internet—Google, Facebook, and other major companies are hard at work figuring out ever-better ways to tailor your web experience to your likes, interests, and preferences. (And, of course, selling the information they gather to advertisers.) The problem, Pariser argues, is that all of this information is being used without our consent, to create a "filter bubble" that we may not even be aware of. How, after all, would you even know if your experience of the internet—the ads you see, the search results you receive when you Google "Santorum"—is the same or different than, say, a Republican housewife from Des Moines?

The primary value of The Filter Bubble comes not in Pariser's argument about the blinkering effects of personalization, or about the threat it poses to creativity or civic life, although those arguments are cogent and compelling. Pariser's biggest accomplishment here is in clearly identifying and unpacking an often unacknowledged aspect of our digital life. As founder Bill McKibben notes in his blurb for The Filter Bubble, "You spent half your life in internet space, but trust me—you don't understand how it works." The Filter Bubble, in language that's rousing and accessible, makes it all just a little bit clearer.