Our purpose is to propose a conceptual model of the growth of knowledge in innovation policy making. We explicitly draw upon evolutionary economics to conceptualize learning as an evolutionary process of the growth of knowledge about policy problems and their solutions. Our model points to the central role of the variation and selective retention of policy alternatives and contributes to the current debate about how to build capacity through and for mission-oriented innovation policies, to address grand social challenges. © The Author(s) 2018. Published by Oxford University Press on behalf of Associazione ICC. All rights reserved.