In most studies of the impact of ethnic diversity on economic growth, diversity is hypothesized to affect growth throughI n 1997, William Easterly and Ross Levine published an article titled "Africa's Growth Tragedy: Policies and Ethnic Divisions" (Easterly and Levine 1997), which found a statistically and economically important negative effect of ethnic diversity on economic growth in a cross-section of countries. Specifically, Easterly and Levine (hereafter E&L) found that moving from an ethnically homogeneous country to one with a diversity of ethnic communities corresponded with a decrease in annual economic growth rates of more than 2 percent. They then applied this finding to Africa, reasoning that, because African countries are typically ethnically diverse, the strong link between ethnic heterogeneity and slow growth was quite likely an important part of the explanation for that region's "growth tragedy." E&L's findings have been broadly accepted. Thanks largely to their article, it is now de rigueur for economists Daniel N. Posner is Assistant Professor of Political Science, University of California, Los Angeles, Los Angeles, CA 90095-1472 (dposner@polisci.ucla.edu).I thank Kanchan Chandra, James Fearon, Asim Khwaja, David Laitin, Drew Linzer, Jean-Laurent Rosenthal, Steven Wilkinson, and two anonymous reviewers for their comments, as well as members of the Laboratory in Comparative Ethnic Processes (LiCEP) and participants at seminars at the World Bank, the Claremont Graduate School, and the UCLA Von Gremp Workshop in Economic History. Drew Linzer, Johanna Birnir, Robert Dowd, Bernadeta Killian, Elin Skaar, Lahra Smith, and Susanna Wing provided valuable research assistance. All errors are my own.