This chapter discusses theories and research on social stratification by gender, focusing on wage and earnings inequalities. The first part describes changes over time in gendered economic inequalities and discusses the various theories used to account for the gender pay gap from demand-side and supply-side perspectives. The division of paid and unpaid work changes considerably when couples have children. The second part of the chapter discusses research on the earnings gap and the theories aimed at explaining why the majority of women, and rarely men, take the parental leave and reduce their work hours when children are young. Finally, the chapter teases out the relevance of these theories by comparing how the transition to parenthood links to relative income development in female same-sex and different-sex couples in the Nordic countries. Findings suggest that the doing of gender and identity formation may be the most important factors explaining birth mothers’ relative earnings development.