- Despite the increasing popularity and use of complementary practice, it is difficult to assess its effectiveness. Lack of research - and lack of agreement on research methods - has led to criticism from branches of conventional medicine. The King's Fund set up an advisory group, chaired by Professor Dame Carol Black, to consider how to develop and apply a robust evidence base for complementary practice. The group drew on the experience of a wide range of academics, researchers, practitioners and funders, much of it shared in a two-day participative conference. This report of the group's deliberations points out that complementary practice presents researchers with a unique set of challenges: how to take account of the context in which the intervention is made, how to reflect the importance attached to treating the whole person, how to accommodate the fact that the relationship between cause and effect may not be straightforward, how to understand "placebo" or non-specific effects. In order for these challenges to be met and overcome, complementary therapy practitioners need to accept the vital role that evidence plays in developing practice. Both conventional and complementary practitioners need to engage in rational debate about the strengths as well as the weaknesses of that evidence. Researchers, funders and practitioners are urged to collaborate in finding a way forward to contribute to our understanding not only of complementary practice but of our ability to manage and sustain health and well-being.