This chapter begins with the extraordinary role lasers have played in medicine, almost from the very moment of their invention in 1960. Initially, laser applications were confined to treating accessible parts of the human body, such as the skin, eyes, mouth, and throat. But with advances in fiber optics, laser beams can now reach deep inside the body, revolutionizing diagnostics and treatment alike. Today, lasers are used in virtually every medical specialty, from oncology and cardiology to ophthalmology and dentistry. Besides offering a basic understanding of how laser light interacts with human tissue, this chapter is designed to provide a comprehensive overview of the many medical applications of lasers in a clear and accessible way.