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The essential basis for a reliable and target-aimed process control is the understanding of the interaction between the laser beam and the treated material and this was gained by thorough research on the influence of the process input parameters on the interaction sub processes and on the treatment result. The main players con-ducting this research over the decades have been research facilities and institutes and this research is still in progress. Since the moment when it was possible to achieve the necessary power density to start the process of deep penetration welding, accompanied by a keyhole, there is hope - and need - to measure e.g. the depth of this vapor channel. In the decades in which the technology of deep penetration welding has been used, various approaches have been developed that allow a measurement of the depth of the keyhole. The aim of this contribution is to show a compact overview on the different approaches to monitor and/or control micro and macro laser welding processes and especially bring out those which successfully have been transferred from laboratory to serial production in the recent past and will be in the near future. Laser materials processing in general offers several possibilities for process monitoring systems or process control but the complexity of the process itself, meaning the dependence of the processing result on several process input parameters, does not facilitate their use. As only continuous supervision of the manufacturing process can guarantee the high demands on the quality of the produced parts, process monitoring systems have become more and more standardized devices in laser applications. There is no doubt that the basis for reliable on-line process monitoring systems is the possibility to measure significant indicators, which demonstrates the instantaneous condition of the interaction zone and/or neighboring areas. This contribution to the Photonics West 2017 LASE conference on the one hand will demonstrate an approach using chromatic coded line sensors for post-weld inspection, on the other hand will show a sensor, based on interferometric principle, which is capable to in-situ measure keyhole depth during deep penetration laser welding and further potential of this sensor approach.