The concept of sustainable tourism development is widely considered to be necessary for successful tourism development, but there is uncertainty over destination stakeholders' understanding and thus ability to implement the concept. Utilising diffusion theory, this paper explores the diffusion of the sustainable tourism development concept among stakeholders in the tourism destination of Kret Island, Thailand. The primary data collection involved semi-structured, in-depth interviews undertaken with 10 local government authorities and 45 local residents, and data were analysed using content analysis. Interpersonal communication was the key channel for the concept's diffusion, and the involvement of opinion leaders, change agents and social networks in this diffusion was explored. Many local residents were laggards in the diffusion of sustainable tourism development thinking in comparison with local government and local opinion leaders. It is argued that both interpersonal and media communication and the identification of key actors in the community are needed to effectively diffuse sustainable tourism ideas among destination stakeholders. The results validate the use of diffusion theory as a means to understand the transfer of the sustainable tourism development concept among stakeholders, and they also provide information useful for the design of information dissemination programmes.