We present a model of household decisions regarding sex, fertility, marriage, and consumption. Households choose marital status based on the expected utility of marriage, and then sex, children, and consumption of other goods to maximize utility subject to a budget and a fertility constraint. An increase in contraceptive efficacy generally leads to increased sexual activity but has ambiguous effects on fertility. Also, increases in contraceptive efficacy lead to lower marriage rates and higher divorce rates. The predictions correspond to the features of the Second Demographic Transition, including declining overall fertility rates, increasing non-marital fertility, and the decline in marriage.