The 29Si high resolution solid state NMR has been used to follow the hydration kinetics of the major component of Portland cement, the tricatcium silicate 3CaO.SiO2(C3S). Experiments have been done also on samples mixed with admixtures or with other cement components like the tricatcium aluminate ЗСаО.Аl2Оз (C3A). The goal of this study is to determine the crystallographical nature of the hydrates which appear in the first minutes after mixing, during the induction period, and evolve till the hardening, in order to have a better understanding of the setting reactional mechanism.