The WHISH trial applies state-of-the science behavioral principles and currently available technologies to deliver a physical activity intervention without face-to-face contact to \ 25,000 older U.S. women expected to consent. It includes the National Institute of Aging (NIA) Go4Life® Exercise \& Physical Activity materials 3 and WHISH developed targeted materials based on Go4Life® to provide inspirational tips and recommendations about how to achieve nationally recommended levels of PA and overcome barriers to exercise, with a means for self-monitoring and setting personal goals. The intervention builds upon evidence-based behavioral science principles and intervention components that have proven to be effective in increasing PA in older women, with innovative adaptive approaches to tailoring the delivery to meet individual (personal) needs.