Over the past decade, the field of health literacy has advanced from providing limited tools for simplifying language into the basis for a viable theory of the complex relationship between knowledge, attitudes, behavior, and health outcomes, ranging from the individual to the societal level. While roughly a decade passed between what seem to be the first (Simonds, 1974) and second (Bee, 1985) appearances of the phrase "health literacy" in peer-reviewed academic literature, the field has more recently experienced very rapid growth in terms of the number of peer-reviewed journal articles. Health literacy is increasingly being described as a theory of behavior change rather than a collection of skills that patients and the public often lack. That model begins with finding, or accessing, information and moves through stages of understanding, evaluating, communicating, and finally using information to make an informed choice. This chapter addresses health literacy, a powerful social determinant of health. Using a program developed by the Canyon Ranch Institute as a primary example, the chapter illustrates how addressing health literacy as a theory of behavior change can produce positive gains in individual, community, and global health. (Contains 1 figure and 1 table.)