How can we design conservation and development projects that produce lasting changes? How can we increase their effectiveness and legitimacy? The classical economic incentives of environmental policies (certification, sustainable forest management, payments for environmental services, green loans, etc.) are effective in the short term, but their environmental performance is not necessarily guaranteed in the long term. However, when the intrinsic motivations of beneficiaries are activated, these beneficiaries take greater ownership of the objectives of actions: they demonstrate more lasting behavioural change. Recent research combining behavioural economics and social psychology, conducted for such projects, is opening a rich and complementary avenue to mobilise this latent human potential. Considering intrinsic motivations implies recognising the importance of the psychological dimension of any action. Research and development decision-makers and donors can and ensure their calls for projects incorporate methods to identify and activate these motivations.