The diversity, equity, and inclusion (DEI) agenda that has captured American institutions in recent years is controversial. While many applaud it on ethical grounds for allegedly redressing past discrimination, critics charge that DEI policies are unfair and damage institutions, including organizations critical to U.S. national security. Until now, however, there has been no systematic study of the operational effects of DEI policies on the U.S. intelligence community. Diversity Dysfunction documents a purposeful effort by the Barack Obama and Joe Biden administrations to reorient the organizational cultures of our intelligence agencies toward the Marxist tenets of DEI and to degrade longstanding and highly effective practices in ways that harm performance. While the damage is readily apparent, we do not yet know the full consequences of the injuries inflicted by the DEI agenda. Our global adversaries have surely noticed the resulting weaknesses in U.S. intelligence but have not yet exploited them. One day, they will. Jettisoning DEI now is our best chance to mitigate the risk.