Historically, research into various diseases and health conditions was conducted exclusively on men, despite the fact that both men and women are affected by a range of illnesses and stand to benefit from the most contemporary treatments. Today, as we aim to conduct inclusive health research and to provide effective, personalized healthcare to all people, we recognize a significant truth: A number of important differences exist between men’s and women’s experiences of health and illness. Some diseases occur more commonly among women, while others disproportionately affect men. Further, men and women frequently experience different symptoms of the same underlying problem or illness (e.g., heart disease), and they often respond differently to the same medications or therapies. To learn more about cardiovascular disease, cancer, diseases of the nervous and musculoskeletal systems, reproductive biology, autoimmune diseases, and so many other conditions, we must accept that the sex of an individual contributes to health and disease in significant ways.