This article contributes to the discussion on the sustainability of the sharing economy by adopting the Social Capital Theory to expand explanations of the sharing economy's role and scope of relations with local communities in the context of overtourism. As mutual relationships have not been fully recognized through a theoretical perspective, the article aims to examine the sustainability of the process of the sharing economy impacting urban tourism communities in light of Robert Putnam's approach to Social Capital Theory. On the basis of a selective systematic review, the article discusses the sustainability of the sharing economy through the lens of bridging and bonding social capital. We argue that a new configuration of social capital, i.e., a sharing platform-modified social capital, arises from the unsustainable and disruptive power of the sharing economy implemented by virtual platforms, thereby contributing to an overtourism syndrome. However, from a medium-and long-term perspective, the sharing economy also impacts the bridging nature of social capital, which should lead to a more sustainable balance in its structure. This initial framework for understanding the impact of the sharing economy on sustainability of local communities provides an alternative approach to studying residents' perceptions and attitudes towards tourism in the areas affected by overtourism.Sustainability 2020, 12, 2310 2 of 26 human and economic activity, strongly emphasizing its presence in the tourism industry, especially in accommodation, transport, catering and tourism experiences [19,20]. As the SE's impact is widely discussed through the prism of accommodation platforms [20][21][22][23] we mostly consider this sector of the tourism industry. Overtourism, in turn, is a place-specific and industry-related mechanism. As a temporary and 'explosive' phenomenon, it condenses all the aspects of visitors' activity and the tourism industry in affected destinations, including the experiences or services distributed or accessed by sharing. Thus, when these two phenomena are studied together, we can discuss tourism as a domain of the SE, and the 'sharing' aspects of overtourism.Yet, due to an early phase of their evolution and the eruptive nature of their expansion, mutual relationships of both phenomena have not been fully recognized, leaving a gap for further research. Even so, many researchers claim that the SE contributes to overtourism by jointly pushing urban gentrification processes, depopulation of city centers and other processes of social exclusion [3,[24][25][26][27][28]. In light of this, in this article we consider overtourism in the context of studying the impact of the SE expansion on local communities. The emerging overtourism syndrome may be one of first striking examples of the problems in which the SE is directly involved. Thus, the externalities resulting from the SE in (over)tourism context on the community level could be a laboratory for SE's influence in general.Although sustainability issues involving the SE have...