Using a sociological viewpoint, this paper examines the range of definitions for complementary and alternative medicine (CAM) and discusses the evidence base for its efficacy and safety. The question of what constitutes evidence is considered from various perspectives: biomedical, CAM, consumers and practitioners. The authors conclude that all these perspectives are required in order to fully understand the appeal of CAM in Canadian society's search for appropriate healthcare. Most important, the complexity of methods for assessing the evidence about CAM is addressed. An inclusive approach is urged that goes well beyond randomized clinical trials. Policy recommendations are made in three areas: research, regulation and funding.