Biocompatibility of dental materials has evolved into a comprehensive, complex, and independent discipline of dental materials science. Materials used in dentistry come into direct contact with the oral mucosa, the pulp, the periapical tissues & the hard tissues of the teeth. Due to the long-term contact, the materials should exhibit a high degree of biocompatibility. Only products with a proven biocompatibility should be used. In this book, the biocompatibility of endodontic materials has been discussed.