BACKGROUND Complementary, alternative, unconventional, and integrative medicine are types of natural medicine that have been known and practiced ever since the recording of history, and in particular in the Old World. This has been rediscovered in many countries, including the New World and especially in the United States. In this review, the philosophical, cultural, and historical aspects are discussed, and the many types of alternative medical practices are mentioned. METHODS The study of complementary medicine shows that evidence required the medical establishment to take unconventional therapies more seriously, and realize that their use alongside traditional medicine, is rapidly increasing. CONCLUSIONS Complementary medicine is a formal method of health care in most countries of the Old World and is expected to become integrated in the modern medical system and to be part of the medical curriculum and the teaching programs of medical institutions as well. Issues of efficacy and safety of complementary medicine have become increasingly important and supervision of the techniques and procedures used is required. More research studies are needed to understand and use this type of medicine.