As part of a research study on collaborative writing, this paper discusses defining and facilitating features that occur during face-to-face collaboration, based on the literature and research. The defining features are mutual interaction, negotiations, conflict, and shared expertise. Facilitating features include affective factors, use of L1, backtracking and humour. Excerpts are selected from the findings of one collaborative writing group in an ESL academic writing class to illustrate the features. The features that occur or emerge during collaborative writing reveal that students are capable of constructing knowledge and developing writing and social skills through interactions with their peers. However, affective conflict may sometimes hinder successful collaboration if not handled appropriately.