We examine time period and generational differences in attitudes toward women's work and family roles in two large, nationally representative U.S. samples, the Monitoring the Future survey of 12th graders (1976-2013) and the General Social Survey of adults (1977-2012). Twelfth graders became more accepting of working mothers and equal roles for women in the workplace between the 1970s and the 2010s, with most change occurring between the 1970s and the late 1990s. Acceptance of dual-income families and fathers working half-time or not at all (stay-at-home dads) also increased. Thus, for the most part, Millennials (born 1980s-1990s) have continued trends toward more egalitarian gender roles. However, slightly more 12th graders in the 2010s (vs. the late 1990s) favored the husband as the achiever and decision maker in the family. Adults' attitudes toward working mothers became more egalitarian between the 1970s and the early 1990s, showed a small backlash in the late 1990s, and then continued the trend toward increased egalitarianism in the 2000s and 2010s. In hierarchical linear modeling analyses separating the effects of time period, generation/cohort, and age, trends were primarily due to time period with a generational peak in egalitarianism among White women Boomers (born 1946-1964). Policy makers should recognize that support for working mothers is now a solid majority position in the United States and design programs for working families accordingly.