Transferring health care research into policy and practice is a messy and complex process which both policymakers and researchers can struggle with. A potential solution is to use individuals or organisations as knowledge brokers. Using a range of literature, this paper explains the theory behind knowledge brokering, identifies three models of brokering and explores the challenges of brokering. We suggest that clarifying these factors is a significant step towards planning well designed and rigorously evaluated brokering interventions. We also suggest that a clearly defined theoretical framework could help us to find out more about how brokering works and its effectiveness.