Laser transmission welding of plastics is a joining technology that has seen a tremendous success story over the last 15 years. With the increasing number of laser-welded applications in such fields as automotive, medical and consumer electronics, the demand for laser-optimized polymer grades is creating big opportunities for plastics suppliers. This lecture aims at presenting the crucial factors that are necessary for a successful laser welding process and illustrates the biggest current challenges in the field based on the latest process innovations.