Background: This paper reflects upon the remarkable demographic transformation that has taken place among unions around the world. I establish the study of unions in a historical context with respect to its place in demographic studies in general.

Objective: I assess the similarities and differences across nations among patterns, trends, and differentials in the determinants and consequences of both marital and nonmarital unions. I focus on data from the United States and a number of other nations, mostly from Europe. Among the vast changes that have transpired over the course of the past several decades I pay special attention to demographic aspects of same-sex unions, as viewed through recently available data, and compare them to the dynamics of opposite-sex unions.

Methods: I draw upon research conducted by others to examine several global trends and differentials in union formation and dissolution. Further, I explore what constitutes ‘dissolution’ in the United States, and for whom. In addition, I discuss the impact of divorce on the economic well-being of spouses in the United States, with particular emphasis on the relative severity of the consequences for women versus men, as well as the factors underlying this differential.

Conclusions: Given the notably broader diversity of unions in the world today, the work of demographers has become substantially more complex than was the case years ago. That complexity notwithstanding, it is especially gratifying that we are rapidly accumulating data with which we can assess the dynamics of all unions, and not merely those of the marital or opposite-sex variety.