During the past decade, the Cochrane Collaboration has been an increasingly important source of information on complementary and alternative medicine (CAM) therapies. From 2007 to 2008, the Cochrane CAM Field developed a topics list that allowed us to categorize all 396 Cochrane reviews related to CAM (as of The Cochrane Library, Issue 4, 2009). This topics list is an advance in making Cochrane reviews on CAM topics accessible to the public. In this article, we discuss challenges in developing the topics list, including developing an operational efinition of CAM, deciding which reviews should be included within the CAM Field's scope, developing the structured list of CAM Field-specific topics, and determining where in the topics list the reviews should be placed. Although aspects of our operational definition of CAM are open to revision, a standardized definition provides us with an objective, reproducible, and systematic method for defining and classifying CAM therapies.