The Transition Network is a global grassroots network that supports community-led resilience in the face of global change. This paper reports on an ethnographic study of one of its longest-running projects, Transition Town Lewes (TTL) in the United Kingdom. The aim of the study is to analyse TTL as a community. More specifically, we ask two questions: (1) what type of community is TTL? and (2) what are the challenges TTL faces as a community? With this, we contribute to the existing literature on local sustainability initiatives and in particular on Transition initiatives, by providing an in-depth understanding of the challenges and social dynamics at play in a day-to-day setting. We conducted three months of intensive ethnographic fieldwork using participant observation, interviews, and a focus group. Our analysis shows that TTL is a community that, on the one hand, is motivated by explicit intentions and goals, but that, on the other hand, leaves openness and flexibility regarding the level and specifics of participants’ engagement. We introduce the novel concept of ‘light intentional community’ to describe this type of community. We first investigate intentionality in TTL, finding that differences exist between individual participant motivations and stated TTL objectives. We go on to describe the ‘light’ aspect of TTL—the differences in levels of engagement between community participants. Our analysis shows that TTL and its participants face two main challenges. First, TTL participants experience ‘multi-dimensional liminality’: they operate in a liminal space between mainstream society and TTL practices, and additionally experience a continuous sense of transitioning toward a moving goal. Second, TTL as a community faces internal and external frictions. These challenges are interrelated and stem from the structure and dynamics of TTL as a light intentional community. We conclude by reflecting on our analysis of the nature and challenges of ‘light intentional communities’, identifying what opportunities this concept brings for overcoming the challenges of grassroots globalization initiatives amidst mainstream society.