Dentin bonding is discussed both in terms of the substrate and in terms of newer bonding systems that have recently been marketed. The most popular bonding systems are presented along with several new systems from Germany and Japan. Etching of dentin is discussed in terms of both its advantages and its disadvantages. Bonding systems can be used to repair fractured teeth as well as to restore carious teeth. This area of knowledge is rapidly expanding. Most of the new products are improvements over their predecessors.