To reduce the technique sensitivity, an adhesive system for resin restoration was recently developed, and changes were made from a 3-step adhesive system to 2-step and 1-step adhesive systems. In this review, the components used as each bonding procedure for each adhesive system, the role of each component, and its efficacy were verified. Furthermore, based on information on the efficacy of acidic monomers to demineralize tooth components, the ultrafine structure of calcium salts of acidic monomers, the hydrogen bonded interactions that additional functional monomers formed at the resin/tooth interfaces, and the bonding mechanisms of 1-step and 2-step adhesive systems to the tooth components, were discussed. The problems caused by the simplification of the bonding procedure were then discussed.