Life-table estimates indicate that one-quarter of U.S. women intend no more births by age 25, one-half by age 27, and three-quarters by age 30. The resulting long period at risk of unwanted fertility is argued to be an important underlying dimension of the revolution in attitudes to and practice of sterilization. Life-table estimates are then considered of the timing of sterilization after the last wanted birth. Almost one-quarter of all couples select sterilization within the first year after they have had the number of children they desire. Recent experience would imply that four-fifths of all couples will eventually use contraceptive sterilization. In order to examine the determinants of men's and women's sterilization, logistic regression is used with a polytomous dependent variable: sterilization of the woman, sterilization of the man, or no sterilization within four years of the last wanted birth. Covariates considered are age and parity at last wanted birth, year and duration of marriage at last wanted birth, wife's and husband's education, wife's and husband's religion, whether residence is in a central city, region, pill-use history and timing-failure histories before the last wanted birth, and unwanted birth. Large and significant effects are found for most of these variables, and these effects change in interpretable ways between early innovative behaviour and sterilization during the most recent period when it was widely accepted.