Monitoring of laser processes has been researched actively since the 1980's in several institutes around the world. The goal of process monitoring is to gather information on the process and to improve the understanding of the occurring phenomena, and to use the gathered data to createquality control methods and adaptive, closed loop control of the process. The methods used forlaser process monitoring can be divided into optical and acoustic methods of which the optical methods are more common. Today, monitoring has been commercially applied to even the newest laser processes, e.g. additive manufacturing. For laser welding, the process monitoring has been developed even further and closed-loop systems have been demonstrated several years ago. The improvements in digital camera technology and data processing have resulted in development of systems that use feature recognition for determining certain features of the process. Monitoring systems have developed from simple systems using single sensors to a more sophisticated systems utilizing a multitude of different detectors and detection methods.