Two thousand years ago, the historian Plinius mentioned in his book Naturalis Historia that "the laser is numbered among the most miraculous gifts of nature and lends itself to various applications." This ancient laser was a plant that was used to cure various diseases. During the last 30 years, modern lasers have gradually penetrated the medical arena and they are being used for diagnostic and therapeutic procedures. At the same time, there has been rapid progress in the development of low loss optical fibers for communication systems. This served as the basis for the use of optical fibers in medical applications such as endoscopic imaging, fiber optic sensing, and laser power transmission. Integrated laser-fiber systems as the laser endoscope or the laser catheter will facilitate imaging, diagnostics, and therapy inside the body. These "least invasive" techniques have already been tried clinically in various medical disciplines and are bound to have a tremendous impact on medicine.