In this study, a bioactive glass of eutectic composition based on Ca-3(PO4)(2)-CaSiO3 system was prepared and investigated. It was found that by controlling the nucleation and growth of crystals, a glass-ceramics free from cracks, containing one or two crystalline phases, and of controlled nano- to microscale microstructure can be obtained. Heat treatment of the parent glass produces various calcium phosphates (Ca-deficient apatite and -tricalcium phosphate) and calcium silicates (pseudo-wollastonite and/or wollastonite-2M) plus amorphous phases. By combining a number of experimental techniques like P-31 and Si-29 magic angle spinning nuclear magnetic resonance spectroscopy, scanning and transmission electron microscopy, energy-dispersive X-ray spectrometry, and Rietveld analysis of X-ray diffraction patterns, a crystallization model was derived, capable of explaining the observed structural and microstructural changes. The determination of amorphous or crystalline phases enabled to produce time-temperature-transformation plots. The structural role on the behavior of these materials and its impact on their in vitro bioactivity are also discussed.