This chapter combines the increasing number of studies that pertain to the stereotype embodiment theory (SET) and reflects upon to represent the current state of this theoretical perspective and how it can help explain age stereotypes’ contributions to health and aging. It describes the history, cultural context, and nature of age stereotypes and age self-stereotypes in a largely ageist society. The chapter presents SET, which provides a framework for explaining how age stereotypes are acquired to subsequently influence health outcomes. It discusses replication studies conducted in different countries, as well as meta-analyses, to demonstrate the validity of this theory as well as to illustrate the meaning and impact of its components. The chapter illustrates how SET may be applied to shape future healthy aging research, policy, and practice. Empirical evidence supports the importance of age stereotype self-relevance among older adults.