The thesis draws on a mixed-methods study which empirically and theoretically investigates the ways in which postgraduate students engage in collaborative learning activities facilitated by technology. The research is both significant and distinct in its approach towards understanding how learners engage in real-life computer-supported collaborative learning (CSCL) settings; what enables or hinders learner engagement; and how engagement shapes the learning outcomes. The ensuing findings indicate that learner engagement is embodied in human behaviour, emotions, and reflection and therefore it is described as a multi-dimensional concept. Learner engagement also appears to be a socially distributed phenomenon – rather than a stable student characteristic – influenced by various personal, group-level, and other situational factors, the most prominent of which are captured by the Hierarchical Model of Enablers and Barriers. The study also reveals that learner engagement presupposes purposeful interaction which is presented as an integrative theme capturing the impact of pedagogical design on engagement. Another observation is that particular combinations of student actions, perspectives, and characteristics tend to resurface and therefore may be considered as strong predictors of potential engagement (or disengagement). This finding led to the development of the WISE Taxonomy of Learner Engagement Archetypes which portrays the most universal engagement approaches that emerged within the studied context. Finally, findings seem to suggest that the way students envisage their learning outcomes is driven by the engagement approach each student adopts, and vice-versa. When combined, the proposed model, taxonomy, and conceptualisation of learner engagement collectively define a holistic analytical framework labelled Distributed Engagement Theory. The purpose of this mixed-methods study is to explore, understand, and subsequently explain learner engagement aiming at making an original contribution to existing CSCL literature as well as informing the design of pedagogical models for enhancing learner engagement in CSCL environments within postgraduate education.