The present study examines grammaticality judgment data, production data and acceptability judgment data from 243 Cantonese second language learners and a control group of 12 native English speakers. Research areas concern (a) the role of the first language in the acquisition of be by Cantonese second language learners; (b) the question if properties associated with be remain persistently problematic for Cantonese speakers; (c) developmental stages of the acquisition of be; (d) the relationship between morphology and syntax; and (e) pedagogical implications. No published L2 research has attempted an in-depth theoretical and empirical treatment of both acquisition and teaching subject matters in one single work. This work helps bridge the gap between acquisition theory and language pedagogy research, benefitting not just language learners but language teachers around the world, and all those who would like to witness a collaboration between second language acquisition theory and second language teaching practice in general.