Identity became apparent as an important theme while investigating the role of interaction in the asynchronous discussion forums of an online post-graduate TESOL (Teaching English to Speakers of Other Languages) education subject. Identity emerged through dialogic choices as students projected an impression of themselves, negotiated their positioning within the group, and established what was valued in this context. Without usual face-to-face meaning making cues, what students post to the forums carry the load of what they mean. Discourse analysis of the initial forums using systemic functional linguistics, provided insights into how identity was being constructed concurrently through interpersonal manoeuvring. This reveals a process of multiple identity construction, with the effect of perceived negative identity discussed. The impact of different tasks on identity formation is also considered.