Irrigation Management Transfer and Participatory Irrigation Management (IMT/PIM) remain popular policies with national governments and international funding institutions. However, despite their widespread application as remedies for poor irrigation system performance, the actual effectiveness of transfer programs is still the subject of much debate and contestation. Our study enters these debates on IMT/PIM through a Systematic Review of all available impact assessments of IMT/PIM in Asia, Africa and Latin America published since 1994. In total we reviewed 131 citations, which together provided 230 case studies of 181 separate IMT/PIM interventions. We found the strength of the methods used to infer impact was low or very low in almost all cases. As important, we found that the distribution of studies was unrepresentative, the data analyzed less than ideal, and the specific criteria for determining success frequently unclear. This leads us to question any overall conclusions based on existing impact evaluations. Our overall conclusion is that research to inform future IMT/PIM policy needs to design better assessments of IMT/PIM performance but that this body of literature must also be supplemented by studies that provide insights into IMT/PIM policy practice.