Even though slightly over half of the U.S. population is female, medical research historically has neglected the health needs of women. However, over the past two decades, there have been major changes in government support of women's health research—in policies, regulations, and the organization of research efforts. To assess the impact of these changes, Congress directed the Department of Health and Human Services (HHS) to ask the IOM to examine what has been learned from that research and how well it has been put into practice as well as communicated to both providers and women. Women's Health Research finds that women's health research has contributed to significant progress over the past 20 years in lessening the burden of disease and reducing deaths from some conditions, while other conditions have seen only moderate change or even little or no change. Gaps remain, both in research areas and in the application of results to benefit women in general and across multiple population groups. Given the many and significant roles women play in our society, maintaining support for women's health research and enhancing its impact are not only in the interest of women, they are in the interest of us all.