Coupled women typically have lower earnings than their male partners. This gender income gap within couples has declined over time, but we lack information about the drivers behind the decline. Here, we analyze the role of increased participation in education and the labor market, as well as changes in social policies, on the decline of the gender income gap within couples in West Germany from 1978 to 2011, using Microcensus data. We show that women’s increased labor market participation and their increased transfer incomes are the major sources of the reduction in the gap. Both trends are strongly connected to family policies. We also shed light on the role of men in the overall trend. Their increased full-time premiums and educational attainment are important counter-trends that outweigh the role of increased unemployment and part-time employment levels among men in reducing the gap.