Efficacy trials suggest that depression is preventable in children and adults. However, current depression prevention interventions are not deliverable to the community en masse. The Internet offers an opportunity to deliver tailored prevention interventions such as those based on cognitive behavioural therapy (CBT) to a large audience, cost-effectively, while preserving intervention fidelity and anonymity. The Internet offers distinct advantages for data collection, which can be used to help refine intervention programs. There are no published randomised controlled trials of the effectiveness of the Internet in delivering depression prevention programs. The feasibility and potential effectiveness of the Internet is indicated by research demonstrating the successful delivery of CBT by computer, the use of the Internet in the delivery of CBT treatment, and the effective prevention of obesity and the promotion of exercise using Internet technologies. Possible limitations to public health interventions using the Internet include selective access, the inability to promote the sites to potential users and the issue of uptake once users access the sites. Randomised controlled trials of CBT delivered by the Internet are required.