The application of zirconia, ZrO2, as a biomaterial in medicine started in the early 1980s. Since then, numerous studies have been conducted on this special ceramic material to assess and discover its unique characteristics in practical biomedical applications. Also, zirconia has manifested its extraordinary advantages for use in dental clinical practice since the late 1990s, such as its excellent biocompatibility, good aesthetical appeal and outstanding biomechanical properties. With the development of fabrication methods and more extensive comprehension of this material, zirconia has been employed in more and more dental restorations from single crowns and root canal posts to long-span fixed dentures and, very recently, even as dental implants. However, there are still some drawbacks in its dental applications. Such drawbacks are its relatively weak bonding with porcelain when compared with metal-ceramic system, less reliable bonding with resin-based adhesives, and possible failures caused, e. g., by the effects of low temperature degradation. Although many studies have been carried out on porcelain to zirconia bonding, a thorough understanding of its real mechanism is still far from being achieved. The effects of different treatments before or during the veneering procedure are not clearly elucidated, thus they need further investigations. The aim of this article is to outline the characteristics of zirconia and descriptions of porcelain to zirconia interfacial bonding based on the research conducted in the past few years. (C) Koninklijke Brill NV, Leiden, 2012