Given the prevalence of overweight and obesity, worksite-based health promotion programs have been recommended due to their potential reach and social support impact. Within worksite contexts, many strategies to prevent and treat obesity have focused on educational programs delivered in person or to small groups that target knowledge acquisition and strategies targeted at individuals to improve their dietary and activity practices. These programs have been criticized because they typically reach a small percentage of workers—and seldom those that could benefit most, are of short duration, and have typically small effects that are not sustained. They have also typically been conducted in large worksites that have the greatest resources. The lack of success of these programs may be due to: 1) inadequate intervention intensity, 2) implementation challenges, and 3) a lack of theoretical models as the bases for intervention development. To overcome the limitations of previous research we will conduct a 2 group randomized controlled trial to determine the reach and effectiveness of an extensive intervention that: (a) is based upon sound theory, (b) is delivered primarily through scalable interactive technologies, and (c) leverages the existing organizational and environmental context of the workplace.