Despite its vital role in the modern marketplace, attention has largely escaped the notice of the antitrust community. Existing discourse exhibits a variety of misconceptions and flawed prescriptions. One example is the widely held notion that attention markets necessitate two-sided platform analysis. Another is a marked overemphasis on data-collection practices. Yet another is that human users, viewers, and listeners are “the consumers” in these markets. And a fourth is that competition for attention occurs within one massive relevant market, obviating the possibility that any single firm could exercise market power.In light of nascent enforcement actions against Facebook, Google, and others, these defects require correction. This Article begins by explaining the basic economics of attention markets, which often involve zero-price barter transactions. It turns next to the appropriate antitrust methodology for market definition. Attention markets need not encompass two “sides”; instead, they are best understood as traditional top-down distribution systems. The oft-used SSNIP test is facially unworkable in zero-price attention markets, but the SSNIC or SSNDQ variants may offer some utility. Practical indicia will often be more useful, however, given the unwieldy nature of hypothetical-monopolist tests. Regardless of methodology, courts and enforcers should take care to avoid the “massive market” fallacy espoused by some commentators.As to market power, both market shares and direct evidence can be useful. The three most common methods for assigning shares—time on-site, active users, and advertising revenues—can each shed light on the issue. Wherever available, direct evidence on attention-cost changes and competitive responses (or lack thereof) should play a significant role. Turning to anticompetitive effects, the “attention overcharge” should be a core concern. Recent litigation efforts have framed this harm instead as “lower quality,” an approach that will often be suboptimal. Finally, competition for attention can lead to overuse, overconsumption, heightened racial and gender animus, and other societal ills. In response, courts and enforcement agencies should extend leniency to certain attention-related conduct that might initially appear harmful
