Eucalypt plantations and contract farming for eucalypts have expanded and are now occurring on a large scale despite concerns about their social and environmental impacts. Our analysis shows that Thai policies and land tenure context have been the principal drivers of the adoption of eucalypt tree growing by Thai smallholders. Thai policies and land tenure system are responsible for the current key role played by smallholders in pulp production. Contract eucalypt farming has become critical for the major pulp companies in Thailand to secure the supply of the raw material. Companies use contract farming to promote eucalypts among smallholders who have not farmed them before and secure their supply in a context of strong competition among buyers. None of the impacts of contract eucalypt farming on the environment and on livelihoods in general are well understood yet, and the paper argues that, to inform appropriate policy development, there is a need to explain how contract tree farming impacts livelihoods.