This paper provides an account of the development of online communities at Ultralab for students engaged on masters-level programmes, doctoral research and continuing professional learning. It considers the ways in which the engagement of learners, and their consequent participation, is seen to be dependent on several factors--the learners' perception of purpose, their sense of identity and trust, framing of learning activities, interventions from learning facilitators and tutors, and the information architecture of the learning space. The notion of engagement in this online community in higher education (HE) is explored. The term "community of enquiry" is used to indicate the key purpose of the community--that of practitioner-based enquiry, or research.