Dentine bonding agents are an important clinical contribution to modern composite technology. Important differences exist between the first- and second-generation materials which offer complementary advantages. The second-generation materials offer higher dentine bond strengths at the expense of greater chairside complexity. Indications for the use of both types of material are discussed. The role of smear layer and the primed layer is discussed and the connection is made between bond mechanism and clinical techniques. The clinical criteria, such as retention, microleakage and tooth strengthening, are related to the role of the hard tissue bond.