We document strikingly similar gender differences in financial literacy across countries. When asked to answer questions that measure knowledge of basic financial concepts, women are less likely than men to answer correctly and more likely to indicate that they do not know the answer. Both young and old women show low levels of financial literacy. Moreover, women for whom financial knowledge is likely to be very important—for example widows or single women—also know little about concepts relevant for day-to-day financial decisions. The gender differences are present for very basic as well as more advanced measures of financial literacy. This is important because financial literacy has been linked to economic behavior, including retirement planning and wealth accumulation. Women live longer than men and are likely to spend time in widowhood. Thus, improving women’s financial literacy is key to helping them prepare for retirement and promoting their financial security.