Walking is an important form of physical activity. It is practiced by people of nearly all ages, throughout the world. Walking is an integral part of life, and there is accumulating evidence that it is essential to good health. There are many ways to measure walking including pedometers, accelerometers, trail counters, direct observation, physical activity questionnaires, and transportation surveys. When measuring walking, researchers must be prepared to demonstrate the validity of their instruments. A paradigm for validation in walking research consists of accumulating evidence at three levels or stages. First, the definitional stage involves investigation of prior theory and empirical evidence to describe the nature of walking. The confirmatory stage involves investigations that either confirm or disconfirm the definition of walking. The highest level of validation is at the theory-testing stage, where we examine theories of how walking is related to other constructs, including the outcomes and the determinants of walking. It is important that validation research in the latter two stages (confirmatory research and theory-testing research) is built on directly relevant research at the earlier stages. The articles presented at the conference on "Walking for Health: Measurement and Research Issues and Challenges" suggest future research directions that will increase our knowledge of walking and health outcomes and provide new approaches to get people walking.