There is a growing awareness of the need to transform food systems. Yet successful actions require sound evidence: on the extent, characteristics, and drivers of issues; on the effectiveness of different policy instruments, and their synergies and trade-offs; on how policy proposals would affect stakeholders; and on citizens’ values and preferences. There are considerable evidence gaps on many of these aspects. This paper presents the main findings from the OECD project “Overcoming Evidence Gaps on Food Systems,” which aimed to identify different types of evidence gaps, as well as pragmatic approaches to overcome these. The project explored this question through three “deep dives” on food insecurity and food assistance programmes across OECD countries, gender and food systems, and environmental impacts along food supply chains. Overall, there is a strong case for greater investment in overcoming evidence gaps for food systems.