In recent decades, the phenomenon of insanity has received considerable attention in the social sciences and humanities. However, major studies devoted to this topic in the context of modern Russian history have remained virtually nonexistent. Alexander Kamensky's book is one of the first studies to fill this significant gap. The monograph is based on a collection of documents from the political investigation agencies of the Russian Empire—the Preobrazhensky Prikaz, the Chancellery of Secret and Investigative Affairs, and its successor, the Secret Expedition of the Governing Senate. The author demonstrates how attitudes toward mental illness evolved over the course of the 18th century, their interpretations were revised, and practices for treating the mentally ill evolved. The historian focuses on the causes of mental illness, the forms in which it manifests itself, and the reflection of historical events on the minds of the mentally ill. By examining the investigative cases of more than three hundred men and women from various social strata who committed political offenses over the course of a century, the author clarifies and corrects a number of established historiographic assumptions about the functioning of state institutions and their attitudes toward insanity, as well as identifies the specifics of Russian practices in comparison with those adopted in other countries at the time. Alexander Kamensky, Doctor of Historical Sciences and Professor at the National Research University Higher School of Economics, is a professor at the National Research University Higher School of Economics.