There has been relatively little systematic evidence on how Sector Based Support (SBS) works in practice, and how effective it is in helping countries improve the delivery of their basic services, such as health and education. This Project Briefing is the first of three emerging from a study of Sector Budget Support in Practice, carried out for the Strategic Partnership with Africa (SPA). The findings and associated recommendations fill a significant gap in current aid policy thinking. This Project Briefing provides an overview of the key findings: that SBS is increasingly popular but under-researched; that access to basic services has improved, but not their quality and equity; and that effective SBS requires less ‘traceability’ and more focus on downstream delivery.