This paper investigates the issues surrounding the use of 3D virtual worlds to enhance learner immersion through improved learner engagement. It is based on findings from the JISC-funded DEsign of Learning spaces in 3D Virtual Environments (DELVE) project at the University of Nottingham and the Open University. Given continued confusion about the term immersion, what it means for a learner to be immersed, and the relationship between immersion, presence and engagement, notions of immersion and engagement in 3D virtual environments are explored in the context of previous published studies ranging from virtual reality to psychology. The resultant improved understanding of the terminology is then used as the basis for coding results from a qualitative, inductive analysis of 20 students that undertook a substantive learning task in the virtual environment Second Life. Emergent themes from the analysis identify key factors that act to both enhance and restrict learner engagement in 3D virtual worlds and a set of principles for practitioners who wish to use 3D virtual environments to enhance learner engagement is presented&