In the past years, the number of mindfulness-based intervention and prevention programs has increased steadily. In order to achieve the intended program outcomes, program implementers need to understand the essential and indispensable components that define a program's success. This chapter describes the complex process of identifying the core components of a mindfulness and yoga program for urban early adolescents through the systematic study of fidelity of implementation of the intervention. The authors illustrate the CORE Process [(C) Conceptualize Core Components; (O) Operationalize and measure; (R) Run analyses and Review implementation findings; and (E) Enhance and refine], based on data gained from a mindfulness and yoga intervention study conducted as a community-academic partnership in Baltimore city.