The introduction states the argument and introduces key concepts, including ideas of multitude and political arithmetic, as well as important distinctions, including that between quantitative and qualitative aspects of demographic thought. It briefly surveys past approaches to the history of population as an idea, paying particular attention to Michel Foucault. It then outlines the book’s episodic approach; explains its geographical and temporal scope (England, Ireland and the British Atlantic, circa 1500 –1800); characterizes the range and types of sources used; and describes its focus on the emergence of population as an object of knowledge and qualitative manipulation (referred to as demographic governance), as well as on questions of the locus and limits of power over population (referred to as demographic agency).