Environmental scanning electron microscopy (ESEM) has been used to study the very early pre-induction, and induction physical processes that occur in the hydration of tricalcium silicate. An in situ experimental technique is described which allows direct, real-time observation of the sub-micrometre morphological changes that take place during this reaction. The results of this investigation are correlated with kinetic data obtained by differential scanning calorimetry (DSC). In this way, microstructural evolution has been identified with the stages of very early hydration. Upon first contact with water, a gelatinous coating was seen to form at grain surfaces and a crystalline secondary product was observed at the end of an extensive dormant period. These findings are viewed in the light of previous "wet" and "dry" microscopy studies, and are discussed within the framework of ordinary Portland cement as a possible explanation of induction. Comment is made as to the suitability of environmental SEM for analysis of such materials.