Abstract Chapter 4 shows how to calculate market shares around products and services of the decentralized economy, such as cryptocurrencies, DeFi market makers, mining and staking pools, and exchanges and trading platforms. Market shares are a key proxy for market power, and most antitrust and competition law investigations will attempt to bring market shares into their analysis. The chapter presents various metrics according to which shares can be measured, and explains their suitability but also their limitations. It also discusses factors that complicate or undermine the calculation of market shares in the decentralized economy so that authorities, courts, and scholars know how to evaluate go to findings.