Mountain resort tourism, in particular ski tourism, has brought about significant change to many alpine communities within North America. Providing an alternative to past industries such as ranching, agriculture, mining, and logging, tourism has been heralded by some as a panacea for the revitalisation of what are largely declining economic bases, whilst others have described it as a destructive force that has brought about many economic, environmental, and socio-cultural concerns. Although significant recognition exists within the academic literature regarding the various economic and environmental impacts resulting from mountain resort tourism, there appears to be a lack of detailed and targeted examination of its socio-cultural sustainability. My research addresses this gap within the mountain resort tourism literature by focusing on this often overlooked dimension of sustainability. This is achieved through using social capital as a conceptual lens to examine the networks, norms, and resources that form a part of our everyday socialisation. While social capital has been widely adopted within sociology, its use in exploring tourism phenomena has thus far been limited. This is despite its ability to highlight the various sociological processes and interactions that occur within tourism-dependent communities and how they have been affected by tourism development. Adopting an ethnographic case study design, I immersed myself within the community of Steamboat Springs, Colorado, living and participating in the daily activities of community members for ten months spanning the winter and summer tourism seasons. During this time, I undertook 53 qualitative interviews with a range of community members from various interest areas to help illuminate many of the socio-cultural issues faced as a result of mountain resort tourism. I accompanied these with participant observation of both special events and day-to-day activities, which were recorded in a field work journal. This was alongside photographs that were captured to provide a complementary visual record of my observations and experiences, as well as the analysis of relevant documentation in the form of council and county reports and plans, the local newspaper, local websites, and magazines. Overall, my research identified mountain resort tourism as having brought about a wide range of impacts that have affected the social capital components of networks, norms, and resources in numerous ways. These effects include the strengthening of community bonding networks, the reinforcement of social norms, and the mobilisation of shared resources through collective action; all of which highlight the existence of such positive aspects of socio-cultural sustainability as a sense of community, democratic community participation, collaboration, and empowerment. At the same time, mountain resort tourism was found to have contributed to such negative social capital outcomes as the social exclusion and isolation of newcomers and other marginalised groups within the community, the creation of anti-social norms in response to its many impacts, resource inequities both within Steamboat Springs and between the surrounding communities, and a growing sense of powerlessness. These outcomes appear reflective of the socio-culturally unsustainable nature of mountain resort tourism as they can be seen as negatively affecting quality of life, a sense of community ownership and attachment, the ability and willingness of many community members to democratically and equitably participate, and the likelihood of inter-community collaboration, whilst also exacerbating socio-economic class distinctions. This raises a number of socio-cultural concerns for the community of Steamboat Springs in regards to the long-term sustainability of mountain resort tourism. In particular, my research highlights the importance of more effective tourism governance, with the community needing to address such issues as future community ownership, democratic and equitable community representation, increased government transparency, and the development of intra- and inter-community bridging networks in order for the socio-cultural sustainability of mountain resort tourism to be achieved. At the same time, the potential for social capital to act as a heuristic device to guide the examination of the socio-cultural sustainability of tourism can also be noted. This is because of its ability to go beyond the identification of mountain resort tourism impacts to explore how individuals, groups, and organisations within tourism-dependent communities have responded to tourism development and its effects on their everyday lives, thereby providing a more holistic understanding of tourism sustainability within a mountain resort community context.