It is considered that a number of factors, such as the external social structure, language proficiency, and relative knowledge of the content domain, affect interaction. Therefore, one of the participants is thought to play a more important role in interaction and to dominate the conversation. However, some studies have illustrated that both participants in a conversation actively contribute to interaction regardless of the pre-existing attributes of the participants. This study examines participants’ contributions to establish mutual understandings in interactions between native and non-native speakers and also investigates whether nativeness and topic expertise affect their contributions to the discourse. The data consisted of five tape-recorded interactions between native and non-native speakers of Japanese and were analyzed using collaborative theory. Analysis revealed that both participants, native and non-native speakers, adjusted assumptions about mutual beliefs at any point in interactions, seek what kind of and how much information their interlocutor needed, and coordinated their responses by using acknowledgment, demonstration, completion, and refashioning. At the same time, this study demonstrated that the collaborative theory is an effective tool for the analysis of discourse where non-native speakers are engaged, in addition to where only native speakers are engaged
