Polymer welding with lasers has been demonstrated already several years ago, using preferably CO2 and Nd:YAG lasers; however, it did not become a big market so far, which is commonly accepted to be due to cost reasons and the size of the laser systems. With the appearance of the efficient, reliable, extremely compact and easy to integrate high power diode lasers, this technology undergoes a renaissance and first application in industrial manufacturing environment have been reported. However, our experience has also shown, that technological hurdles still exclude certain applications and limit the technology to certain configurations. This is, since additionally to the material parameters of the polymer for conventional welding, e.g. melting resp. glass temperature, decomposition temperature, thermal expansion coefficient etc. for the laser weld of course optical parameters play a key role.