We conducted a systematic review and meta-analysis investigating the components and effectiveness of self-help weight-loss interventions and their applicability to less-advantaged populations. We searched (November 2013) for randomized controlled trials comparing self-help interventions with each other or with minimal controls in overweight and obese adults, with 6 months or longer follow-up. We calculated mean difference between intervention and control for 6- and 12-month weight change. Twenty-three studies met the inclusion criteria (9632 participants; 39 intervention arms). Intervention participants lost significantly more weight than controls at 6 months (mean difference -1.85 kg; 95% confidence interval [CI]=-2.86, -0.83; 7 studies). No significant effect was detected at 12 months but results were sensitive to the inclusion of 1 study at high risk of bias. Interactive programs appeared more effective than standard ones at 6 months (mean difference -0.94 kg; 95% CI=-1.50, -0.38). Evidence is insufficient to reach conclusions on effectiveness in socioeconomically disadvantaged people, but suggests self-help interventions may be less effective in this group.