The gender wage gap, the disparity in pay between men and women, has narrowed to 81 cents in 2016 from 57 cents on the dollar in 1975. Nevertheless, the gap persists. Over the course of a career, the gender wage gap results in women earning $1 million less than men do. To close this gap, women have relied primarily on the advantages conferred by education. Today, women are enrolling in college in greater numbers than men, breaking through barriers to pursue degrees in male-dominated majors that offer higher earnings, as well as graduating in greater numbers at all levels of education. In the 1970s, the number of associate's degrees awarded to women began outnumbering those awarded to men. In the 1980s, the number of bachelor's degrees and master's degrees awarded to women overtook the number awarded to men. By the 2000s, more women completed doctoral degrees than men. The report explores the complex set of reasons that have kept the gender wage gap in place. Even when comparing men and women who have equal educational attainment and work in the same occupation, women still earn only 92 cents for every dollar earned by men. [For the executive summary, see ED594548.]