Sustainability is a concept used with increasing frequency in tourism development, planning and management circles. It is often linked to terms such as ‘green’ tourism and/or ‘ecotourism’. Despite being used for over a quarter of a century, the term is not well defined and tends to be used as a ‘buzzword’ by commentators, researchers and those in marketing. To a certain extent sustainability is now an overused term and is open to abuse, particularly from those operators who wish to indicate that their product is worthier than another’s. This chapter traces the history of the concept of sustainability and how it has been developed and applied in the context of tourism. It evaluates theoretical perspectives on tourism and sustainability and discusses what sustainability means within the context of leisure and tourism planning in New Zealand. It presents recent United Nations Sustainable Development Goals and also considers why achieving sustainable tourism is likely to be problematic.