Maverick purchasing involves the acquisition of categories from suppliers other than the contracted supplier, or using standards other than the agreed specification, or using processes other than the agreed process. Any of these situations cause spend ‘leakage’, or reduction in the value of spend secured by the contracted suppliers. Suppliers of spend analytics solutions and transactional purchasing systems describe the reduction in maverick spend as a benefit of their solutions. In practice, maverick spend erodes the value of forecast benefits from sourcing decisions, and may affect the confidence of contracted suppliers in the buyer’s volume estimates. However, while some maverick spend is driven by ignorance or rogue decision makers, some stakeholders choose not to use the preferred sources for legitimate reasons, and understanding why ‘maverick purchasing’ is taking place can yield valuable feedback on what stakeholders need and why.