The Women's Health Initiative (WHI), established by the National Institutes of Health in 1991, is a long-term national health study that focuses on strategies for preventing heart disease, breast and colorectal cancer and osteoporosis in postmenopausal women. These chronic diseases are the major causes of death, disability and frailty in older women of all races and socioeconomic backgrounds. The WHI a 15-year multi-million dollar endeavor, and one of the largest U.S. prevention studies of its kind. The study involves over 161,000 women aged 50-79, and is one of the most definitive, far reaching clinical trials of women's health ever undertaken in the U.S. The WHI Clinical Trial and Observational Study will attempt to address many of the inequities in women's health research and provide practical information to women and their physicians about hormone replacement therapy, dietary patterns and calcium/vitamin D supplements, and their effects on the prevention of heart disease, cancer and osteoporosis. Emerging information from the NIH Women's Health Initiative and other studies of women's health begun in the 1990's should be changing the landscape of options for older women in the years to come.