Bioglass® 45S5 is widely used in biomedical applications due to its ability to bond to bone and even to soft tissues. The sintering ability of Bioglass® powders is a key factor from a technological point of view, since its govern the production of advanced devices, ranging from highly porous scaffolds to functionalized coatings. Unfortunately this particular glass composition is prone to crystallize at the temperature required for sintering and this may impair the bioactivity of the original glass. For these reasons, a prerequisite to tailor the fabrication of Bioglass®-derived implants is to understand the interaction between sintering, crystallization and bioactivity. In this work the structural transformations which occur during the heat treatment of Bioglass® are reviewed and a special attention is paid to the sintering and crystallization processes. Moreover the bioactivity of the final glass-ceramics is discussed and some alternative glass formulations are reported.