We present research that the use of ellipsis in English is evidence that users are interacting. Ellipsis is a linguistic phenomenon where we can leave something unsaid and the context allows us to supply the missing part. For example, when someone asks us a question like “Where did you see him?”, we do not need to give a full sentence answer like “I saw him over there”. The context of the question allows us to just give the relevant information that is the answer to the question where, i.e. “over there”. Since ellipsis is contextual in this way, we can suppose that the phenomenon is interactive by nature. Many strategies have been discussed in the literature which are used by speakers to interact, and this is an issue that is very much discussed in literature on computer-mediated communication. Peterson (2009) analyses data from textchats by Japanese learners of English and identified a series of strategies that show that interaction is taking place. These include back channel support (continuers), giving and seeking help, correction of self and others, and off-task discussion. Darhower (2002) discusses greeting/leave-taking, intersubjectivity (maintaining and developing a discourse topic) and use of a speaker’s first language (if not already the main language of the discourse). Repetition is discussed by Cogo (2009: 260), Suvimiitty (2012, chapter 7) and Mauranen (2012: chapter 7) in discourses involving speakers of English as a Lingua Franca. These strategies suggest that the learners are creating and maintaining social cohesion, and lead to the formation of discourse communities. We analyse data from textchat logs that come from my own corpus of seminar discussions from an online MA programme in English Linguistics, also involving non-native speakers of English. We show that the intersubjectivity, repetition, continuer and correction functions can be found in our data set, and we propose one more: comments. Intersubjectivity is by far the most common function as we might expect from seminar discussions, while continuers and corrections are very rare. The use of these functions clearly marks that students are interacting as members of a discourse community.