I just finished reading David Bernstein’s new book–Classified: The Untold Story of Racial Classification in America–and highly recommend it to anyone interested in the development of modern United States laws involving racial and ethnic classification.

Bernstein, a professor at Antonin Scalia Law School, walks the reader carefully through the modern history of racial and ethnic classification, starting in 1964. Interestingly, he explains how today’s laws involving racial and ethnic classification trace, with only minor modifications, to an obscure 1977 order of the Office of Management and Budget, “Race and Ethnic Standards for Federal Statistics and Administrative Reporting,” known as Statistical Policy Directive No. 15, or simply “Directive 15.” Directive 15 contained a disclaimer that its “classifications should not be interpreted as being scientific or anthropological in nature,” and that they should not be “viewed as determinants of eligibility for participation in any Federal program,” like affirmative action programs. Nevertheless, Directive 15’s racial and ethnic classifications are the de facto standard for federal, state, and local governments and the private sector, including in medical research.

Today, the Directive 15 classifications are: American Indian or Alaska Native, Asian, Black or African American, Hispanic or Latino, Native Hawaiian or Other Pacific Islander, and White (the original 1977 categories were American Indian or Alaskan Native, Asian or Pacific Islander, Black, Hispanic, and White). While these categories may not seem controversial to many readers—in part because these are the boxes that Americans are so accustomed to checking—Bernstein’s book explores each category in detail, explaining the often arbitrary distinctions made at their boundaries. For example, Pakistan is the dividing line between “Asian” and “White”: Individuals of Pakistani descent are “Asian,” whereas their neighbors from Iran are “White.”

As Bernstein explains, because the Directive 15 categories are incorporated into numerous affirmative action and other racial preference programs, any potential revision to Directive 15 is the subject of intense lobbying, such as the unsuccessful attempt to establish a Middle Eastern category in the 1990s. Groups currently receiving racial and ethnic preferences often do not want those benefits diluted by the expansion of preferences to other groups, and there are sometimes ugly debates as to how to define the new group (such as whether Israeli Americans should be included in a potential Middle Eastern category).

Bernstein’s book is particularly timely as the Supreme Court considers in its upcoming term the constitutionality of affirmative action at Harvard and the University of North Carolina. The current justification for affirmative action is to promote “diversity” on college campuses. While a laudable goal, Bernstein’s book explains that within the racial categories typically excluded from preferences in college admissions—White and Asian—there exists incredible diversity. And many individuals one might not think of as “diverse” nevertheless get to check a box that entitles them to preferential treatment. It is a bizarre world, for example, where a group of students consisting of a white student of U.K. descent, a white student of Spanish descent, and an individual of 1/256 Cherokee descent is considered more “diverse” than a group consisting of a white student of Bosnian descent, a student of Iranian descent, and a Hasidic Jew (the first group has only one “White, non-Hispanic” student, whereas the second is all “White, non-Hispanic”).

While “diversity” is the legal rationale for affirmative action in colleges, I suspect that many proponents of affirmative action are also motivated by another laudable desire: rectifying past discrimination and improving social and enonomic mobility. Here, too, Bernstein’s book is informative. He notes, for example, that many or most Black students at various elite universties are not American Descendents of Slaves (“ADOS”) or Black Americans who have suffered from generations of discrimination in this country, but instead relatively wealthier international students and first-generation African or Carribean immigrants.

Relatedly, the recent release of “Economic Mobility Index Ratings of American Colleges” by the liberal Third Way think tank is striking. Six of the top ten universities with respect to economic mobility were part of the California State University system, notwithstanding the fact—or perhaps because of it—that those universities have been legally prohibited by California’s constitution from granting preferential treatment to any group on the basis of race, sex, color, ethnicity, or national origin for over 25 years.

Bernstein’s book focuses on helping the reader understand the development of modern racial classifications in the United States, not on debating affirmative action or other racial preferences—although I did get the sense that Bernstein thinks that racial preferences would be more defensible if they were focused on ADOS and members of Native American tribes. But to have an informed debate about the merits of affirmative action and other racial preferences, it’s important to first understand how our racial classifications developed and how they operate in practice. On this score, Bernstein’s book is a must-read.