Trust is indispensable for social and economic relations; it is the glue that holds organisations together and appears to work somehow mysteriously. Overall, trust is a ubiquitous ingredient in policymaking and implementation across many governance systems including education, whether it concerns accountability mechanisms, capacity building or strategic thinking. Yet our understanding, conceptualisation and measurement of these issues remain limited. This working paper asks the question: what is trust and how does it matter for governance, especially in education systems? It explores why trust is key for policymaking and where it fits within current governance issues. The paper examines different definitions of trust, presents various ways of measuring trust and discusses some of their benefits and limitations. It proposes a definition of trust made up of three parts: trust as an expectation, a willingness to be vulnerable and a risk-taking act. The paper then presents a simple model of trust and governance and reviews the relationship between trust and different elements in education systems, such as complexity, asymmetries in information and power, collaboration/cooperation, monitoring and accountability, and professionalisation. It concludes with some policy findings and identifies several research gaps.