Polylactide (PLA) is one of the nature based polymers, which is already commercialized for several applications, but it is still strongly under research and development concerning both the polymer basis and the processing technology to overcome some material immanent disadvantages and to ensure optimal structure-property relationships. Because PLA shows a very slow crystallization behavior under high cooling rates - like usual in injection molding - it tends to solidify in the amorphous state that is resulting e.g. in insufficient heat resistance. Crystallization can be accelerated by nucleation agents or subsequent annealing after injection or even ejection from the mold. The influence of injection molding parameters as well as the effect of annealing on the structure formation as well as thermal and mechanical properties have been investigated for several PLA grades. Additionally, also the influence of several nucleating agents was considered. It could be shown that the annealing procedure has a dominant influence on crystallization, structure formation and property level, respectively, if crystallization takes place during heating from the solid amorphous state. Furthermore, it could be shown that PLA crystallization, starting from the melt, can be effectively triggered, if the so called stereocomplex can be generated during melt processing by combination of the stereo-isomers D-lactide and L-lactide. The stereocomplex crystals act as nucleator for the common PLA and increases the degree of crystallinity, and - because of their higher melting temperature - contribute essentially to the improved heat resistance of the material.