In our article entitled “The Political Science 400: A 20-Year Update” (PS, January 2007, 133–45), we presented the names and total citation counts (1960–2005) of political science faculty employed (ca. 2002) in U.S. Ph.D.-granting institutions who were among the 400 most cited in their cohort or subfield. We recognize the very important nature of our data for individual scholars and the institutions at which they teach, and we apologize to those colleagues whose citation counts were misreported, especially to those few whose counts were off by a very large amount. Yet, given that nearly 4,000 political scientists are employed in a Ph.D.-granting institution in the U.S., and given the numerous data limitations associated with using the Web of Science search engine (as we explained in the lengthy methodological appendix to our article), while we worked as hard as we could to prevent errors, having some errors in our data set was virtually unavoidable.