Understanding the complexity of the historical demographic transition—the secular change from high to low levels of mortality and fertility in Western Europe and the United States during the nineteenth and twentieth centuries—has long been a major goal of historical demography. Recent developments in individual-level life-course databases and longitudinal statistical models have allowed scholars to test ever-more complex hypotheses about the causal factors in demographic change and to develop an increasingly fine-grained image of demographic behavior before, during, and after the transition. Such studies are critical for identifying variation, both between and within societies, obscured by secular trends that appear uniform at the macro-level, and for distinguishing the contingent elements of demographic change from the universal elements. The six articles presented in this special issue bring new substantive and methodological insights to the field of historical demography—revealing the responsiveness of pre-transition fertility to changing contexts, tracking the transmission of new fertility practices, exploring the unevenness of mortality and fertility decline, and documenting the changing role of social institutions in family formation.