Antitrust has again become a hot topic in U.S. policy discourse. There are lots of contributing reasons:  Online firms have grown large and ever more important in many individuals’ lives. Media references to “Big Oil”, “Big Pharma”, “Big Tech”, etc., have become more common. The Obama Council of Economic Advisers issued a 2016 report that highlighted rising seller concentration—and related concerns about rising market power—in many sectors of the U.S. economy. These concerns have been echoed by The Economist and by a number of academic and “think tank” studies. There have been efforts to link this increasing size and concentration to wage stagnation and worsening income distribution.

The term “monopoly” is heard far more frequently today than was true even a decade ago.

Antitrust is one of the major policy tools in the United States—along with direct regulation—designed to address monopoly and more generally the exercise of market power. For the financial sector, regulation of various kinds generally overshadows antitrust. But even for the financial sector, antitrust plays an important role: indeed, in June 2018, the U.S. Supreme Court decided an important antitrust case that involved American Express’s relationship with the merchants that accept its payment card.

So, let’s first review some basics about antitrust. We’ll next describe the recent trends in company sizes and seller concentration. And we will then move on to the relevance of antitrust for the financial sector….