This qualitative multi-case study explores a group of university-based language teacher educators' boundary crossing experiences in Hong Kong. Informed by a conceptual framework on boundary crossing and drawing on data from in-depth interviews and field observations, the findings reveal the opportunities and challenges embedded in teacher educators' boundary crossing between university and schools, between the teacher education and academic community, and between local and external contexts. The study contributes new knowledge to our understanding of teacher educators' boundary crossing through two different forms, i.e., horizontal and hierarchical, as they navigate sociocultural differences between various communities. The paper concludes with practical implications on how to promote teacher educators' continuing development in university settings.