In flexible labour markets, capital increases the productivity of skilled workers more than that of unskilled workers, and in the US faster investment is associated with wider wage inequality. But labour market institutions that keep unskilled workers’ wages high also imply that firms may find it profitable to invest so as to boost those workers’ productivity. Our empirical analysis based on industry-level data confirms that a higher capital intensity in Germany is associated with smaller wage differentials and with a larger share of unskilled workers in the labour costs. Changes in capital–labour ratios during the 1980s reduced wage differentials by 5–8% in German industries, while in the US capital deepening in such industries as machinery and retail was accompanied by an increase of wage differentials larger than 7%.— Winfried Koeniger and Marco Leonardi