Lightweight constructions are currently of high interest for several industrial applications, like automotive, shipbuilding and aerospace, in order to meet the environmental requirements according to the reduction of the CO2-emissions. This demand can be met by replacing heavier material with lighter ones. One of the resulting relevant dissimilar material combinations is made of steel and aluminum alloys. However, the welding of these material combinations is characterized by a poor weldability, due to different physical properties and the formation of hard and brittle intermetallic phases, which may lead to cracks. The laser welding may be more suitable compared to other fusion welding process, due to its specifically advantages regarding high welding speed, low distortion and the controlled melting of the both different materials. In addition, owing to prominent strength and stiffness properties, continuous glass and carbon fiber reinforced composite structures are recognized as having a significant lightweight construction potential for a wide variety of applications. The use of composites based on thermoplastic matrix materials is a growing trend in particular in the aerospace sector. Significant advantages of this material class compared to thermoset systems are nearly unlimited storage times of semifinished products, flame retardant properties, higher impact tolerances and mainly the weldability. In this context, laser welding of thermoplastic composite parts becomes increasingly important as a controllable and reliable joining technique. A novel generation of thermoplastic stiffening panels has been developed, consisting of hybrid composite structures, which are based on a carbon fiber reinforced supporting structure and a glass fiber reinforced face sheet. Application examples and further potential of these laser technologies for lightweight construction will be presented.