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Privacy scholars have extensively studied online behavioral advertising, which uses Big Data to target individuals based on their characteristics and behaviors. This literature identifies several new risks presented by online behavioral advertising and theorizes about how consumer protection law should respond. A new wave of this scholarship contemplates applying fiduciary duties to information-collecting entities like Facebook and Google.

Meanwhile, lawyers—quintessential fiduciaries—already use online behavioral advertising to find clients. For example, a medical malpractice firm directs its advertising to Facebook users who are near nursing homes with bad reviews. And, in 2020, New York became the first jurisdiction to approve lawyers’ use of retargeting, one form of online behavioral advertising. But the professional responsibility scholarship has not yet considered these developments.

The Article describes the rise of online behavioral advertising and lawyers’ nascent use. It draws on modern privacy scholarship to explain how this advertising method can lead to privacy invasions and manipulation. It then explores the specific case of lawyer advertising. And it critiques the existing regulations, which do not prohibit tactics involving privacy invasions or manipulation even though they undermine client autonomy—a key concern for the law of lawyer marketing.

In addition to this descriptive and doctrinal work, the Article makes two other contributions. First, the examination of online behavioral advertising helps explain why the legal profession struggles to integrate new technological innovations more generally. AI tools and similar products are driven by informational capitalism’s focus on exploiting knowledge advantages, its speed, and its scale. But these features all are in tension with traditional aspects of the fiduciary relationship between lawyers and their clients. Second, as privacy scholars begin to think about how the duty of loyalty might provide a principle to limit abuses of Big Data in other contexts, the Article proposes that lawyers—who already have this duty—make good subjects for a case study.