This article disaggregates change in adolescent fertility between 1971 and 1979 into four components: change in marriage patterns, in nonmarital sex, in pregnancy, and in birth. It also assesses quantitatively the relative contribution of each component to the change over time in two fertility outcomes: the probability of a nonmarital live birth and, given a live birth, the odds of its being nonmarital. The changes in the probability of sexual debut prior to marriage and in marriage patterns themselves are the two most important contributors to these changes. The influence on the change in adolescent fertility outcomes of the decreased likelihood of marriage following a nonmarital pregnancy was compensated for by the increased use of abortion to terminate the pregnancy.