This longitudinal case study explored how four Chinese university students constructed their global and national identities while learning English and using it as a lingua franca in the course of four undergraduate years. Qualitative research methods were adopted. Primary data were obtained through open interviews, and supplementary data sources included student journals, classroom observations, and Internet postings. Analysis showed that the students constructed multiple kinds of global identities and a prominent Chinese national identity in their engagement with ELF. The national and the global were often dialogically related. The ELF-associated identities, particularly the global, were often embedded in their membership in selected communities of practice and imagined communities. The students were also found to exercise their agencies in choosing their target communities. The study showed both the pervasiveness and variation of identity work with ELF.