Purpose: Today's technology supports the design of more and more sophisticated interactive learning environments. This paper aims to argue that such design should develop from first principles. Design/methodology/approach: In the paper by first principles is meant: learning theory and principles of course design. These principles are briefly outlined, key features of which include: the use of knowledge and task analysis methodology; the use of topic maps; and learning design that supports adaptive teaching. The paper goes on to describe how this approach to course design has been applied at the UK Defence Academy. Findings: The paper shows how conversation theory serves as a source of first principles for the design of interactive learning environments, as exemplified in the Course Assembly System and Tutorial Environment (CASTE). Originality/value: A principled approach to the design of interactive learning environments is of value in bringing order to a conceptually and methodologically confused domain of practice. (Contains 6 figures.)