It is rare for antitrust issues to reach public consciousness, but the question of what to do, if anything, about the dominant Internet firms of the day has clearly done so. The GAFA, as they are known in Europe—Google, Apple, Facebook, and Amazon, and let’s throw in Microsoft for good measure—have each achieved a remarkable market position in the technologies that seem to define so much of the modern economy, especially the consumer-facing economy. While each of these companies benefits from dynamics of platform economics, these firms are interestingly different and it is important not to lose sight of that as we consider possible regulatory responses to their market positions.

The rules of competition and antitrust are perhaps most important at the point where we have competition in a market adjacent to a market held by a dominant firm, especially where there is the promise that the adjacent market could turn into a springboard for competition back into the original market. Adjacency matters as it is quite difficult to attack a dominant firm in its home market, though even that might be possible if we have a leading firm in one market entering the market of another dominant firm.

Here, I look at the two most developed examples we have of the role of antitrust in adjacent market competition in platform industries. We have an extensive history for Microsoft and a now growing one for Google. Both situations show the difficulty of achieving meaningful remedies even when antitrust violations are found.

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