The National Institutes of Health Women's Health Initiative (WHI) is the largest research study ever funded by NIH ($625 million over 14 years) and is designed to test strategies to prevent cardiovascular disease, breast cancer, and osteoporotic fractures—leading causes of death, disability, and decreased quality of life for older women. Although the WHI has already begun, serious questions remain about its design, cost, and the likelihood that it can answer the questions it asks. This book evaluates whether the effort can be justified scientifically.