The formation of common law marriages and consensual unions has long been part
of the marital structure of Mexico. This type of unions increased markedly during the
last decade in Mexico including its northern border region. This region is intriguing-
ly heterogeneous because in some states the proportion of cohabitation is as high as or
even higher than that of marriages, whereas in others this proportion is still much
lower than that of marriages. It is interesting to note that the levels of lower to higher
proportions of consensual unions in the region run from east to west and from south
to north