Ricken, StephenBarkhuus, LouiseJones, QuentinLewkowicz, MyriamRohde, MarkusMulder, IngridSchuler, Douglas2019-04-042019-04-042017978-1-4503-4854-6Event-Based Social Networks assist the coalescing of groups for social activities. In this paper, we present a mixed-method study of Meetup organizers' experiences coordinating events. Through a survey of 100 Meetup groups and interviews with 13 organizers of Meetup groups, we describe their organizational practices and challenges as well as potential longer-term success factors. We emphasize motivations and factors both in terms of social and technological issues. We discuss how these organizers build and maintain social capital but also how they rely on their already existing community leadership capabilities. We conclude that organizers had four different reasons to start a group through Meetup and describe each in turn. Our research contributes to a better understanding of how event-based social networking platforms can be designed and built to support coalescing within niche interest groups.enEvent-Based Social NetworksGroupwareLeadershipMeetupSocial MediaSocial SoftwareSocializingText/Conference Paper10.1145/3083671.3083705