The paper presents findings from the first-ever systematic review of the causal impact of development aid on violence in countries affected by civil war. The review identifies 19 studies: Fourteen within-country studies from Afghanistan, Iraq, Colombia, Philippines and India, and five cross-national studies. These studies investigate the impact of six aid types: Community driven development, conditional cash transfers, public employment scheme, humanitarian aid, infrastructure and aid provided by military commanders in Iraq and Afghanistan. The evidence for a violence-dampening effect of aid in conflict zones is not strong. Aid in conflict zones is more likely to exacerbate violence than to dampen violence. A violence-dampening effect of aid appears to be conditional on a relatively secure environment for aid projects to be implemented. A violence-increasing effect occurs when aid is misappropriated by violent actors, or when violent actors sabotage aid projects in order to disrupt the cooperation between the local population and the government.