In advanced microsystems various types of devices (metal-oxide semiconductor field-effect transistors, bipolar transistors: sensors, actuators, microelectromechanical systems, lasers) may be on the same chip, some of which are 3D structures in nature. Therefore, not only materials combinations (integrated materials) are required for optimal device performance of each type but also process technologies for 3D device fabrication are essential. Wafer bonding and layer transfer are two of the fundamental technologies for the fabrication of advanced microsystems. In this review, the generic nature of both wafer bonding and hydrogen-implantation-induced layer splitting are discussed. The basic processes underlying wafer bonding and the layer splitting process are presented. Examples of bonding and layer splitting of bare or processed semiconductor and oxide wafers are described.