Tourism is one of the fastest-growing industries in the world and bears significant weight in global economic terms. However, there are concerns about the sustainability of the industry from an environmental and social/cultural perspective. One of the world’s top ten international tourism destinations, Thailand, had a record-breaking 39 million international tourists in 2019 but is expected to fall to around 14 million in 2020, the lowest level in 14 years, due to COVID-19. These impacts can be especially severe in small tropical islands where the land base is small, resources scarce, and local populations have low incomes and limited opportunities for livelihood diversification. Especially amid a global pandemic and the impending risks of climate change, it is crucial to reset, carefully consider concerns about sustainable tourism development, and move forward with management regimes that better embrace sustainability principles. This thesis examines the application of sustainable tourism using Koh Phangan, Koh Samui, and Koh Tao in the Gulf of Thailand as case studies to aid in sustainability planning for the future, particularly for island tourism destinations. Data were collected using a standardized questionnaire administered to 1261 tourists visiting the three islands during the peak tourism season (January to March) of 2018. The findings are presented within this thesis in three papers. The first paper focussed on the behavioral approach and compared visitors to each island, noting differences in tourist demographics, travel characteristics, motivation factors, and areas of management concern identified. The second paper focussed on the limits of acceptable change approach and used cluster analysis of visitor motivations to identify three types of visitors that were described in terms of the specialization concept: Cluster 1 (“very high importance generalists”), Cluster 2 (“high importance generalists”), and cluster 3 (“mixed importance”). While cluster 1 had the greatest mean importance scores for all environmental, social, economic, and logistical factors, it identified the most areas of concern whereas cluster 3 identified the least. The third paper explored scenario planning as a vehicle for sustainable tourism planning on the island of Koh Phangan and was framed within the Tourism Area Life Cycle (TALC), Tourism Opportunity Spectrum (TOS), and Ecotourism Opportunity Spectrum (ECOS) models. Most respondents preferred the “green scenario” in terms of accessibility, amount of visitors, development, food and accommodation, transportation around the island, traffic, waste management, water storage, and the scale of tourism. Collectively, these findings suggest that tourists can play an important role in identifying management priorities and that tourists tend to support a more sustainable tourism industry, as opposed to a focus on “mass tourism”, sometimes referred to as “sun, sea, sand” tourism. The study argues for adopting place-based planning practices and creating educational opportunities to ensure that the benefits of tourism are not outweighed by the costs. Especially as the tourism industry continues to expand, there is often a push to enhance visitation and the economic benefits that tourism provides; however, it is important to consider the environmental, social, economic, and logistical capacities of a tourism destination. / Graduate / 2021-08-21