Abstract Informed by Complex Dynamic Systems Theory, this study examines the nature of homestay as a situated language learning site, with an eye toward the development of American student guests and Chinese host families’ homestay experiences within the larger context of the study abroad (SA) program and local community. Drawing on data collected from host families and student guests, this study discovers benefits, conflicts, and co-adaptations in homestay; the evolution of host families’ dispositions toward homestay; student guests’ proficiency gains and interactions with hosts and locals; and contextual factors that influence the proficiency gains and interactions. The findings reveal that homestay is a dynamic, self-evolving subsystem, which constantly interacts with other dynamic subsystems, such as the SA program and local community, within the complex social ecosystem of the entire SA environment. This study also provides suggestions for the design and management of the homestay component in the SA program and future research.