Polymer product properties are determined by intrinsic molecular features and, to a great extent, the thermo-mechanical conditions during product shaping. Much work on this topic has been dedicated to classical processes (extrusion, injection molding etc.) but similar effort is required for additive manufacturing processes as the same issues apply. The goal of this work is to develop the required models and experimental methods and procedures to bridge the gap between processing conditions and the final mechanical properties for Selective Laser Sintering. This includes full characterization and modelling of the multi-phase crystallization of PA 12, including the effect of post-condensation, comparison between intrinsic mechanical properties and those obtained for specific SLS conditions. The mechanical part focusses on yield stress and life time predictions. These tools should help to understand and improve the performance of SLS products in relation with polymer features and processing conditions, and to make different experimental results comparable.