Foucault argued that, starting at the end of 18th century, the object of power becomes biological life; politics becomes "biopolitics." He claimed that statistics plays a major role in that change. We explore those arguments, while testing a third: biopolitics takes as its object not so much real as probable lives. Starting with Pascal's "wager" on the afterlife and Leibniz's "palace of destinies," we discuss modern demographics, statistics as a political science, and later developments, from theories of civil safety to techniques for valuing (and devaluing) lives, exploring the ethical and political questions they raise.