This inquiry originates in a conversation between the first two authors which concluded with the challenge that a Revans Institute for Action Learning & Research should not only be doing research "by" action learning and but should also be researching "into" action learning itself. Action learning has been a recognised innovation in management education and development in the UK since a major initiative undertaken in the General Electric Company in 1975. Since then interest in action learning has waxed and waned without it either becoming widespread or disappearing. It has continued to develop within a practitioner community associated with Professor R. W. Revans, who is credited as the founder. Action learning has been controversial, especially because of its championing of the ideas of practitioners or action learners over those of experts and teachers. This article summarises the authors' findings to Spring 2004. The provisional tone emphasises the limitations of research that is confined to action learning in the UK. Without expecting to deliver a complete "fix" on the extent, growth and variety of UK action learning, the authors hoped to establish a benchmark for future research and also to promote the use of action learning in UK business schools and higher education. Given the wide variations of practice to be found in the UK alone, they decided to stick to what they knew best, and exclude, for example, practice in the USA and Asia, which, according to reports, has expanded greatly in recent years. (Contains 6 figures.)