To communicate effectively in policymaking systems, actors need to understand how policymakers process evidence and the environment in which they operate. Therefore, we combine psychology and policy studies to produce a three-step strategy. First, do not bombard people with evidence. Human beings have too much information to process, and they use heuristics to filter information to make decisions quickly. Synthesise and frame evidence to help you tailor it to the ways in which policymakers demand and understand information. Second, find the right time to act. Timing matters during key individuals’ patterns of thinking and the alignment of conditions in political systems. Third, engage with real world policymaking rather than waiting for a ‘rational’ and orderly process to appear. To present evidence during mythical stages of a ‘policy cycle’ is misguided, and to ‘speak truth to power’ without establishing legitimacy and building trust may be counterproductive. Our overall message is pragmatic, not Machiavellian: effective communication requires the suppliers of evidence to see the world from the perspective of their audience and understand the policy process in which they engage.