The rise of cohabitation and the growing share of births to cohabiting couples have led to speculation that the boundary between marriage and cohabitation is blurring. We examine this issue with an analysis of the financial arrangements of fathers of mainland Puerto Rican children. The analysis shows that married fathers are more likely than cohabiting fathers to pool their income, but this difference does not result from socioeconomic and demographic factors that foster uncertainty. The analysis also demonstrates that income allocation methods are generally stable over time after differences in union dissolution by allocation method are considered. The discussion emphasizes the need for research on the ways that financial ties reflect and reinforce the bonds between partners.