Written between 1912 and 1979, Carl Schmitt’s diaries (published and unpublished) rank among the most illuminating documentary sources of the era. This chapter argues that the published diaries have significantly transformed perceptions of his personality, motivations, and sentiments as well as of his thoughts on crucial intellectual and political questions related to 20th century Germany. Drawing extensively on these primary sources, the chapter finds a consistency between his candid private perspectives and the ideas articulated in his major publications, thereby seriously challenging several pervasive interpretations of Schmitt’s thought and work regarding cultural pessimism, political theology, the “Conservative Revolution,” and war. While documenting his antisemitism, the diaries also confirm his often intimate, complex relationships with Jews. Among other significant insights, the chapter argues, Schmitt did not seek to undermine Weimar or realize his theories in the “Third Reich.” Few documentary collections have ever required such a momentous reevaluation of a historical figure.