Technical Abstract: Obesity and chronic disease risk factors are rising among youth. The Internet offers promise as a channel for delivering behavior change programs in a manner that is both available and accessible. This manuscript describes how theory informed the development of an Internet-based program promoting the maintenance of healthy eating and physical activity (PA) behaviors to 8-year-old African American girls. The web site was designed using a theoretical framework composed of Social Cognitive Theory (SCT) and the Elaboration Likelihood Model (ELM). Program content was developed to target mediating variables derived from SCT, whereas the delivery channel was designed to enhance central processing, a concept derived from ELM. This manuscript is important because interactive multimedia provides a promising medium for attracting and maintaining youth's attention, thereby enhancing the opportunity for behavior change to occur. Such interventions can incorporate state of the art theory-based procedures, effect behavior change, and provide opportunities to test theoretical constructs and procedures. Further, it demonstrates that theory-based behavior change programs can be developed and delivered over the Internet with expectations of success.