This report addresses the polycentric governance of blockchain systems, following conversations held from September 2022 until September 2023 by a reading group of blockchain practitioners and academics. The ERC-funded BlockchainGov project led the reading group. Since the publication of the Bitcoin whitepaper in 2008, blockchain technology has gained increasing popularity for being a “decentralized” ledger of transactions. Collectives of people have formed to discuss and decide on—to “govern”—the evolution of blockchain networks and blockchain-based applications, creating what we refer to as “blockchain systems.” While much literature is dedicated to understanding the governance of blockchain systems, no substantial efforts have been made to apply the concept of “polycentricity” to blockchain governance. Polycentric governance systems are characterized by multiple autonomous decision-making centers with overlapping areas of responsibility, which both compete and cooperate within a common overarching system of commonly agreed-upon rules, spontaneously or deliberately generating a shared social order. A term initially presented by Michael Polanyi and famously further developed by Vincent and Elinor Ostrom, polycentricity allows us to understand blockchain systems' structure, process, and outcome.