The introduction presents the “police intellectuals” and explores their attempts to modernize the department, motivated by the fear that a rapidly diversifying New York City had become terra incognita, or unknowable space, because of immigration. “Police intellectuals” were people in politics, police departments, the press, or universities who thought collectively about ways of addressing crime in the late nineteenth- and early twentieth-century city. These thinkers not only built a department that explicitly centered race and ethnicity in its operations but they also laid the foundation for the operation of the modern police department.