What do birthdays mean? Why are they so obligatory for modern people? Based on neo-Durkheimian perspectives on ritual, this article suggests the anthropological history of the western birthday as a key to understand its meaning. The article points at the unique ritual system developed by modern industrial culture, such as birthdays, jubilees, and other anniversaries—designated here as Rites of Temporality—which latch on to the numerical milestones marking the passage of time to which the celebrant (individual, institution, settlement, state, and so forth) is subject. Comparing the birthday with classical rites of initiation then reveals how over and above individualism, consumer culture, state bureaucracy, and historical consciousness, the birthday honors time’s most noticeable markers since the industrial era—numbers—thus objectifying conventionalized time as a central meaning maker for modern people.