Structural knowledge of bioactive glass systems is necessary to understand their biological properties and improve their mechanical and clinical performance. In this work, the local structure of P and Si in bioactive glasses of the system CaO-SiO2-P2O5-CaF2 with different Mg or Sr contents was determined, by means of P-31 and Si-29 magic-angle sample-spinning nuclear magnetic resonance (MASS NMR) and Raman spectroscopies. The results show that phosphorus is located in calcium-orthophosphate domains, surrounded by silicate species containing 1, 2 and 3 bridging-oxygens per SiO4 tetrahedra. The type and relative distribution of the silicate units do not depend on the nature of the alkaline earth cations present in the system. However, the increase of RO content decreases the degree of polymerization of silicon tetrahedra, while PO4 monomeric units remain unchanged. An interpretation of the medium-range structure of the glass is suggested.