There is substantial epidemiological evidence that widespread adoption of specific behavior changes can significantly improve population health. Yet, health communication efforts, while well intentioned, have often failed to engage people to change behavior within the complex contexts of their lives. `E-health communication', health promotion efforts that are mediated by computers and other digital technologies, may have great potential to promote desired behavior changes through unique features such as mass customization, interactivity and convenience. There is growing initial evidence that e-health communication can improve behavioral outcomes. However, we have much to learn about whether the technical promise of e-health communication will be effective within the social reality of how diverse people communicate and change in the modern world. This article examines current evidence concerning e-health communication and evaluates opportunities for e-health applications.