Objective: Trauma, with resultant bleeding, is a significant cause of morbidity and mortality throughout the world, however the best possible method of bleeding control by immediate responders is unknown. We performed a systematic review of the effectiveness of treatment modalities for severe, life-threatening external bleeding in the out-of-hospital first aid setting. Methods: We followed the Cochrane Handbook for Systematic Reviews of Interventions methodology and report results according to PRISMA guidelines. We included randomized controlled trials, non-randomized comparative studies and case series investigating adults and children with severe, life-threatening external bleeding who were treated with therapies potentially suitable for first aid providers. We assessed the certainty of the evidence and risk of bias. Outcomes were prioritized by first aid specialists based on importance for patients and decision-makers and included mortality due to bleeding, all-cause mortality, cessation of bleeding, time to cessation of bleeding, a decrease in bleeding and complications/adverse effects. Results were reported in Evidence Profiles. Results: Of the 1,051 full-text articles screened, 107 were included for analysis including 22,798 patients. The primary methods of bleeding control were tourniquets (n=49), hemostatic dressings (n=34), hemostatic devices (n= 14), pressure dressings/bandages/devices (n=8), pressure points (n=4), including two studies that reported multiple hemorrhage control methods. Overall, certainty of evidence was very low and often relied on indirect evidence and poorly controlled studies. Tourniquets were associated with a decrease in mortality when compared with direct manual pressure. Hemostatic dressings resulted in a shorter time to hemostasis than direct manual pressure using standard dressings. Direct manual compression resulted in a shorter time to hemostasis than pressure dressings/devices. Conclusion: Overall, data regarding the control of life-threatening bleeding is of very low certainty, making it difficult to draw robust conclusions for treatment by immediate responders. While more robust data is needed on first aid treatments of life-threatening bleeding, this systematic review aggregates the most comprehensive to date to help guide recommendations.