This article examines the evolving significance of formal marriage and of partner selection in nineteenth-century Santiago do Iguape Brazil. Across social divides, racial and class endogamy were the norm for marriage partners, but consensual unions were far more likely to unite couples of different races. The information about enslaved couples was more sporadic, but I found that most slaves married partners who shared their country of origin, and that there was a higher slave-marriage rate on larger plantations. My research suggests that free and enslaved people constantly violated the borders separating them within a stratified plantation society, but that formal marriage retained a special significance and was reserved for unions between social equals.