The purposes of this tutorial are threefold: (a) to clarify the meaning of measurement validity, (b) to provide appropriate validation procedures for use by researchers in adapted physical activity, and (c) to raise the awareness of the limitations of the traditional views on measurement validity. Several validation procedures are described with specific examples from adapted physical activity research based on traditional approaches of providing validity evidence. Conceptual and empirical limitations of the traditional validity framework are discussed. We recommend that several categories of validity evidence should be reported in research studies. We encourage practicing the unified concept of measurement validity (Messick, 1993, 1995) in adapted physical activity research and practice.