After a first book on the liberalization of trade in the European Union, Michelle Egan’s new effort compares EU market building with the emergence of national markets in the United States. This book joins a burgeoning literature on federalism in transatlantic perspective, but is distinctive in mobilizing Egan’s expertise in regulation and law in order to focus more specifically than any other major contribution on “single markets.” These are political projects that aim to facilitate exchange across existing regulatory jurisdictions by erasing barriers, standardizing rules, and/or replacing disparate regulations with new central ones. The core of Single Markets sets broad case studies of the “four freedoms” enshrined in the EU treaties—of goods, capital, services, and labor—alongside evolution of the same “freedoms” in the nineteenth-century United States.

Egan’s main goal is to persuade us that these processes display many parallels, despite their different time periods and contexts. The general point is that single-market projects raise similar issues and wrestle with the same challenges. In support of this contention, the author marshals a very impressive range of literature and evidence across historical eras and scholarly divides. She identifies three key commonalities.

“First,” Egan summarizes in the conclusion, “the fact that governments can—and do—strongly influence how markets work is crucially important in understanding economic developments in the US and EU” (p. 237). In broad terms, she portrays single markets as state-centered agendas, with political projects of institutional authority shaping market developments more than they respond functionally to economic conditions.

Second, “markets need to be differentiated as the specific characteristics of each factor market can yield different degrees of integration” (p. 237). U.S. and EU markets have become most liberalized and unified in goods. Capital-market integration has also gone far in both places, though more haphazardly; much remains to be done in Europe, and the U.S. case has long retained very fragmented features. (For example, only in 1994 did U.S. states surrender the ability to bar other states’ banks from opening branches.) In services and labor, the advance of single-market integration is still more erratic and seemingly idiosyncratic. Taking transport as her main focus, Egan details how this sector led the way in integrating the American market—with the railroads physically connecting the country and also serving as test cases for broader regulatory shifts—while in Europe, the integration of transport has lagged behind many other sectors. In labor, where Egan focuses on the issue of professional qualifications and occupational licensing, the EU single market has decisively surpassed the American one. Professions in the United States are regulated by states, with only a patchwork of mutual-recognition compacts or national professional standards sometimes facilitating free movement. Egan suggests that these barriers have actually increased over time as occupational licensing has spread to new sectors: Today, interior designers need licenses in Florida and three other states, but not elsewhere, and hunting guides need a license only in Colorado (p. 208). Meanwhile, the EU has systematically constructed rules that facilitate the cross-state recognition of licenses and degrees. Thus, the qualifications of lawyers, architects, dentists, engineers, haircutters, and most other professionals are accepted more easily across Finland and Portugal than across Ohio and Pennsylvania.

Third, single-market projects create social and distributional problems and tend to depend on participatory and democratic processes to continue successfully. This is Egan’s most diffuse theme, since she wisely refrains from formulating it as a tight functionalist claim: Rather than insisting that market making only proceeds in measure with participatory legitimation, she just notes that such steps have pervasively elicited opposition. Single-market initiatives have sometimes paid off, circumvented, or ridden over such challenges; sometimes they have been blocked. In any case, would-be market makers had better be ready for countermobilization and distributional fights.

Egan’s arguments for these parallels across the U.S. and EU cases are compelling. Specialists of either polity will learn much from the comparative perspective, and even experts on comparative federalism will encounter rich troves of new observations. What they can take away in analytical, theoretical terms is a bit fuzzier. Besides making the case for comparisons, the book also aspires to explain “what accounts for the success or failure in creating integrated markets” in these two polities (p. 2), but Egan’s commitment to this goal wavers as she proceeds. The broad and rich empirics never quite gel around a sharp sense of what precisely is being explained or what distinct explanations we might offer for it.

As in much of the literature on market integration, Egan’s analysis is blurred by uncertainties over whether she wants to explain regulatory change or economic behavior. A single market, strictly defined, is a regulatory outcome: rules that facilitate exchange across preexisting borders. The main reason we care about such regulations, however, is that they usually affect economic behavior. If federal polities adopt more single-market regulations, the story goes, then exchange expands, competition sharpens, innovation rises, prices drop, and we see dynamic growth. Yet exchange and mobility on the ground can also happen without single-market regulations. Where we find cultural and linguistic connections, complementary resources, and adequate transport and technology, we may see considerable mobility and exchange across fragmented regulatory jurisdictions. Conversely, even the most fluid single-market regulations may not shift economic behavior very much across cultural or logistical barriers. Even if Finnish dentists can legally practice more easily in Portugal than Ohioan dentists can in Pennsylvania, there is more mobility and more of an integrated market for dentists across American states than across EU countries. If Egan recognized this and specified clearly that she is trying to explain regulatory frameworks—single markets per se, not market flows—she could better focus her explanatory enterprise.

Specifying the explanandum would offer more of a target for sharper debates between explanatory schools, allowing the author’s rich research to speak more directly to what is at stake when we think about single markets. As it is, she distills four explanatory approaches from a vast range of scholarly literature, but they do not coalesce into distinct hypotheses that could motivate a consequential debate over her evidence. Some scholars have focused on evolving legal ideas as the causes of single markets, others on business and interest-group pressures, others on political projects in state authority, and others on distributional coalitions. All these elements surface periodically in the case studies, but never quite in a form that could ground a distinct explanatory claim that one of them (or some particular combination) explains EU or U.S. outcomes especially well. Opportunities to raise explanatory debates frequently drift by. For example, in perhaps the clearest and most intriguing contrast between the polities—EU liberalization of professional qualifications versus “nineteenth-century practices of local economic regulation” in the United States—we hear simply that “the political realm [of the US federal government] has not actively intervened to mitigate state power,” (p. 199) though the constitutional Commerce Clause offers the legal basis to do so. Have the “feds” left professional qualifications untouched due to legal ideas, interest groups, conceptions of state authority, or distributional concerns? Egan’s deep knowledge of these cases should put her in a good position to tell us more.

Overall, Single Markets assembles a wealth of knowledge on history, public policy, law, and economics to help us better understand the core workings of two huge economies that still dominate our world. We can look forward to the ways in which Egan and others will build on these foundations.