There are tradeoffs in knowledge synthesis--for example, between comprehensiveness and timeliness, between generalisability and policy relevance. The tradeoffs are particularly challenging for public health. A growing international community is grappling with building more relevant and useful knowledge bases, to facilitate use of this knowledge in policy and practice. These questions guided a knowledge synthesis using a novel "rapid review" methodology. The synthesis used complex adaptive systems as a theoretical lens, in collaboration with an international expert panel. Findings strengthen the call for a systems paradigm in public health, extending theoretical propositions to empirical studies of knowledge generation and use.