Successful interaction makes sense to its participants – it is, in other words, coherent. As different resources are employed to indicate mutual orientation by showing which actions are linked and where attention is paid, coherent conversation can be said to be achieved multimodally. This thesis builds on an interactional and ecological theoretical basis, and investigates how strategies for sense-making vary depending on the context of interaction.

Specifically, this is a study of interaction in different types of multimodal and multiplex communication situations. The characteristics of these technology-rich communication situations are mapped and, primarily through ethnographic methods and interaction analysis, it is investigated how conversational coherence is maintained. Furthermore, it is suggested how the findings can be applied to inform interaction design.

The analysis presented is based on results from four case studies, dealing with different aspects of coherence creation in different English speaking contexts. Study 1 investigates coherence in intertwined threads in dyad instant messaging (IM) interaction, and Study 2 focuses on coherence through conversational feedback strategies in interaction in a multimodal desktop video conferencing system. Study 3 has a somewhat broader focus, as the multiple communication channels in which one participant is involved are all taken into consideration in the investigation of sequential coherence. Finally, in Study 4, the physical and digital interaction in a partly shared studio space is investigated, with an emphasis on how mutual orientation is established during conversation initiation.

The findings show that when addressing coherence it is important to acknowledge both dynamic aspects of context, such as activity and participants, and more static aspects, such as communicative affordances of environments and tools. In online and mixed-mode interaction, the notion of context becomes particularly complex, as participants are simultaneously part of both the individual context, which may include digital tools for communication, and the shared context of interaction (polycontextuality). In this thesis, it is further shown that this has consequences for coherent conversation initiation and possibilities to engage in multiple semi-simultaneous conversations (polyfocality). Additionally, the results emphasize the importance of explicit linguistic strategies in computer-mediated interaction.