No one disputes that ads are a critical part of the Web's information ecosystem. News Web sites like this one depend on them for nearly all their revenue, as do sites like Facebook and YouTube that have changed the way we communicate online. What generates a lot of debate are the increasingly sophisticated methods for selling ads targeted to narrow segments of Web users. Today, Web sites ranging from tiny blogs to newspaper publishers to digital giants such as Google engage in a practice called behavioral targeting, a method of compiling data about which sites people visit, what topics they search for and an array of other Web activities to better surmise what types of ads might prompt them to make purchases.
