Many colleges and universities nationwide have experienced an influx of international students in the recent years. International students have become important research subjects. Yet, little is known about their out-of-class learning and how that affects their overall learning experiences in the USA. The objective of this five-month qualitative study was to investigate the informal social interactions between ESL learners and their native speaking counterparts. The theoretical framework was built upon Gumperz's interactional sociolinguistics (1982). Data include fieldnotes, interviews, participant observations, participant diaries, and artifacts collected from the participants. The representation of data followed Spradley's (1979) hourglass design: grand tour, domain analysis, and in-depth analysis. Microethnographic discourse analysis was used to analyze the transcripts of the participant observations, which were obtained from the video and audio recordings of their social interactions. The findings suggest that participants engaged in three key kinds of learning in out-of-class settings: (a) language learning moments, (b) recontextualization of cultural knowledge, and (c) negotiation of social identity. The findings also suggest that ESL freshmen construct multiple levels of dorm identities, which are critical for them to become legitimate participants in the campus communities.