Abstract Assessing complementary and alternative medicine (CAM) use remains difficult due to many problems, not the least of which is defining therapies and modalities that should be considered as CAM. Members of the International Society for Complementary Medicine Research (ISCMR) participated in a Delphi process to identify a core listing of common CAM therapies presently in use in Western countries. Lists of practitioner-based and self-administered CAM were constructed based on previous population-based surveys and ranked by ISCMR researchers by perceived level of importance. A total of 64 (49%) ISCMR members responded to the first round of the Delphi process, and 39 of these (61%) responded during the second round. There was agreement across all geographic regions (United States, United Kingdom, Canada, and Western Europe) for the inclusion of herbal medicine, acupuncture, homeopathy, Traditional Chinese Medicine (TCM), chiropractic, naturopathy, osteopathy, Ayurvedic medicine, and massage therapy in the core practitioner-based CAM list, and for homeopathy products, herbal supplements, TCM products, naturopathic products, and nutritional products in the self-administered list. This Delphi process, along with the existing literature, has demonstrated that (1) separate lists are required to measure practitioner-based and self-administered CAM; (2) timeframes should include both ever use and recent use; (3) researchers should measure and report prevalence estimates for each individual therapy so that direct comparisons can be made across studies, time, and populations; (4) the list of CAM therapies should include a core list and additionally those therapies appropriate to the geographic region, population, and the specific research questions addressed, and (5) intended populations and samples studied should be defined by the researcher so that the generalizability of findings can be assessed. Ultimately, it is important to find out what CAM modality people are using and if they are being helped by these interventions.