The Women's Health Initiative (WHI) is a major research program launched in 1991 by the National Institutes of Health to address health issues affecting postmenopausal women. It aims to identify the most effective strategies for preventing heart disease, breast and colorectal cancer, and osteoporosis. The initiative includes clinical trials and observational studies involving diverse groups of women across the United States. The WHI has provided valuable insights into the effects of hormone therapy, diet, and lifestyle on women's health. Its findings have influenced medical guidelines and public health policies, helping to improve the overall health and well-being of women as they age.