Cohabitation, as a relationship form, is becoming much more common in the United States. Approximately half of the persons currently in their 30s cohabit prior to marriage and more than half of all recent marriages were preceded by cohabitation between those marrying. Through the use of in-depth interviews I studied the transition between this new form of "dating" and the traditional course of marriage. Couples who cohabited with each other prior to their marriage were interviewed about how they made the transition to marriage. Couples' perceptions are what changed in the transition from cohabitation to marriage. The transition comes about through the passage of time, through external events which make an impact on the couple's relationship, and through beliefs about what certain events and behaviors mean. / Ph. D.