|Abstract:||The demographic behaviors of one generation, including marriage, divorce, fertility, and survival, create the population of families in which the next generation of children is raised. Assortative mating between men and women with varying socioeconomic characteristics is a key mechanism in establishing the families of the next generation, but differential fertility, child and parent survival, marital disruption, and parents' socioeconomic mobility modify these marriage patterns. This article examines the demographic mechanisms through which family backgrounds are created. It presents the mathematical links between marriage patterns and the joint distribution of parents' characteristics when their children are born and later in their lives. It illustrates these relationships using data on educational assortative mating, fertility, mortality, and the living arrangements of families in the United States. Although the educational attainments of husbands and wives are strongly associated, patterns of differential fertility reinforce this relationship, resulting in an even strong association between the educational attainments of mothers and fathers.