This book chapter provides a theoretical and empirical overview of student engagement as it applies specifically to open, distance, and digital education (ODDE) contexts. The authors review the major theoretical foundations of student engagement — including Astin’s involvement theory, Community of Inquiry, Self-Determination Theory, and Community Theory — and present their own working definition of engagement as the energy and effort students invest across behavioural, cognitive, affective/emotional, and social dimensions. A key contribution is the application of a bioecological model (adapted from Bronfenbrenner) that situates the student at the centre of nested systems (micro, meso, exo, and macro levels), with the chapter focusing especially on the meso and micro levels as they relate to digital learning. The authors highlight the persistent “fuzziness” of engagement as a construct in research, the under-theorised role of social engagement in ODDE, and the importance of treating disengagement as a separate construct rather than simply the absence of engagement. The chapter concludes with open questions and a research agenda for the field.