There is increasing awareness of a need for rigorous research into complementary and alternative medicine, but as yet, limited guidance has been given to researchers, practitioners and students as to the range and scope of the various methodologies available and how existing methods can be modified for CAM research. This research methods series provides an outline of the main methods for researching CAM-related issues, including clinical trials, cross-sectional studies and qualitative methodologies. Drawing on the experiences of a range of experts in CAM research, each article in this series addresses the scope and strengths of a particular methodological approach. This series aims to convey the basis and objectives of particular methodologies within the context of CAM research, and thus, each paper will draw on actual examples of CAM research. It is intended to be of value both to inexperienced researchers and to those who are more experienced but are looking to broaden their range of knowledge. In this introduction, we outline some of the fundamental concepts for researching CAM, providing an overall sense of where each methodological approach outlined in this series fits in the 'order of things'. We outline different design strategies, the philosophical differences underpinning particular approaches to collecting data, and the issue of bias in research design and analysis.