Semiconductor wafer bonding has increasingly become a technology of choice for materials integration in microelectronics, optoelectronics, and microelectromechanical systems. The present overview concentrates on some basic issues associated with wafer bonding such as the reactions at the bonding interface during hydrophobic and hydrophilic wafer bonding, as well as during ultrahigh vacuum bonding. Mechanisms of hydrogen-implantation induced layer splitting (''smart-cut" and "smarter-cut" approaches) are also considered. Finally, recent developments in the area of so-called "compliant universal substrates" based on twist wafer bonding are discussed.