The system of nuptiality probabilities for never married males and females, the “marriage regime,” is viewed as a population transformation, which operates on a population thereby changing the composition. The marriage regime has many properties common to other population transformations, but embodies a constraint such that, in general, the marriage regime cannot be strictly stable over time. The approach is applied to study the “marriage squeeze,” the alteration in marriage patterns that results from an imbalance in the “marriage market” or numbers of never married males and females at the usual marriage ages. Using data on age at first marriage for the 1960 American white population, nuptiality probabilities by single year of age and sex are estimated for the years 1915–58. Annual estimates also are made of the relative number of eligible mates (never married of the usual marriage ages) for never married persons of a given age and sex. No close correspondence is found between annual fluctuations in the marriage market and in the nuptiality probability, possibly because of the crudeness of the estimates. Alternatively, response to the imbalance may take another form such as marriage postponement or a redefinition of eligibility.