Counterintelligence history has too often relied on a “wilderness of mirrors” trope, which suggests that the discipline is driven by personalities and self-delusion. Using the newly available Vassiliev notebooks and other sources, this article takes a closer look at the historical evolution of U.S. and Soviet counterintelligence as they developed and changed tactics in response to a changing world and the evolving actions of their opponents. Although blind at times to one another, they moved—especially on the American side—toward greater clarity of the opponent and a more complex approach to counterintelligence, driven by real-world experience and a growing knowledge of the threat posed by the other side.