This ethnographic study-cum-action research documents the cultivation of a community of practice for sustainable professional development among a group of 18 teachers of English as second language in Hong Kong through a series of planned efforts over 10?months. By juxtaposing the theory-driven planned efforts and the spontaneous actions and interactions of the teachers, we aim to chart the way or ways teachers learn and develop as a professional and as a community of practice. Extrapolated from field notes, reflective journals, position papers, and evaluative comments, the authors learn that sensitivity, self-awareness, honesty, and facilitation helped iron out tensions and dissonances arising out of different personalities and different teaching approaches. Unexpected group synergy arising from interactions of experienced and novice teachers, and of teachers from different backgrounds helped bring out the expertise from each teacher. Yet, their communal responsibility faded when they returned to their respective schools. Selected experiences demonstrate that sustainable teacher professional development requires strong individual commitment and support from schools, parents, and the wider educational community.