With rising rates of obesity and obesity-related health problems, finding additional means to help reduce obesity is critical. This review examined the impact of the Internet as a medium to deliver weight loss programs. Specifically, the review examined the public’s interest, the availability and the known efficacy of Internet-based weight loss programs. Findings showed that the general public is turning to the Internet for diet and fitness information and has reported that information they found online has impacted their behaviour. Little is known about who is interested in using the Internet for weight loss and what their experiences have been. The programs most readily available to the general consumer tend to vary widely in quality, with few efficacy studies. However, researchers have shown that efficacious programs have been delivered via the Internet. Successful online programs included a structured approach to modifying energy balance, the use of cognitive-behavioural strategies such as self-monitoring, and individualized feedback and support. Implications include developing strategies to increase distribution of programs with known efficacy, determining the applicability of effective programs for diverse audiences, conducting media literacy education for the general public, and continued research into understanding who may be best served by online weight loss programming.