Women make up over half the U.S. population, but historically have been underrepresented in clinical research supported by the National Institutes of Health (NIH) and others. As a result, differences in the manifestation of certain diseases and reactions to treatment in women compared with men were not identified. For example, there have been instances of women having adverse effects that differed from those of men related to medications and other treatments. NIH’s Inclusion Policy established requirements governing women’s inclusion in its clinical research. This book examines women’s enrollment and NIH’s efforts to monitor this enrollment in NIH-funded clinical research; and NIH’s efforts to ensure that NIH-funded clinical trials are designed and conducted to analyze potential sex differences, when applicable.