This article discusses the role of market definition in competition analysis, including complexities regarding analysis for digital markets (e.g. the SSNIP test relies on pricing data, but digital markets often involve zero price products), and alternative market definition tools regarding such markets. Also discussed is whether market definition tools require an overhaul in the digital context and that effectively regulating the digital sector is considered an area of high priority by regulators such as the US Federal Trade Commission and Department of Justice, the European Commission, and the Australian Competition and Consumer Commission.