There are key differences between mind-body medicine and alternative medicine. A central tenet of mind-body medicine is the recognition that the mind plays a key role in health and that any presumed separation of mind and body is false. Alternative medicine, however, does not focus on the role of thoughts and emotions in health and, therefore, is separate from mind-body medicine. Also, while there has been little scientific research on alternative medicine, the literature on mind-body medicine comprises more than 2000 peer-reviewed studies published in the past 25 years. The groundwork for understanding the physiology of mind-body interactions was established by pioneering studies in the 1930s by Walter Cannon, and in the 1950s by Walter Hess and by Hans Selye that led to an understanding of the fight-or-flight response. Later work by Holmes and Rahe documented measurable relationships between stressful life events and illness. Other research has shown clinical improvement in patients treated with a placebo for a variety of medical problems. The effectiveness of placebo treatment can be interpreted as compelling evidence that expectation and belief can affect physiological response. Recent studies using spectral analysis and topographic electroencephalographic (EEG) mapping of the relaxation response demonstrate that by changing mental activity we can demonstrate measurable changes in central nervous system activity. These, and other, studies demonstrate that mind-body interactions are real and can be measured.