This paper gives a brief description of the Okapi projects and the work of the Centre for Interactive Systems research, as an introduction to this special issue of the Journal of Documentation. Okapi is the name given to an experimental text retrieval system (or rather, family of systems, as will be discussed below), based at City University, London. The current systems and their predecessors have been used as the basis for a series of projects, generally addressing aspects of user information‐seeking behaviour and user‐system interaction, as well as system design. The projects have been supported extensively by the British Library, and to some degree by a number of other funders. They have been at City since 1989; for the previous seven years they were based at the Polytechnic of Central London (now the University of Westminster). In order to give a picture of the system(s) that now constitute Okapi, it is appropriate to describe one version containing some of the features that have become central to the Okapi projects, and then to indicate the variety of systems now implemented or implementable within the present setup, as well as the directions it may go in the future. In what follows, papers in this issue are referred to by brief titles.