This paper presents an in situ study of the hydration of cement pastes in the SEM, made possible by the development of a radical new technology for the investigation of wet samples: the QX capsule from QuantomiX, based on the WETSEM technology, consists of an electron transparent but water and air tight membrane, which allows the examination of cement/water suspensions without any further preparation. In this way the evolution of hydration can be followed dynamically - in the same sample - over time. Results obtained with this technique are described. In addition to plain water/cement pastes the impact of additives on the early formation of phases has been studied. The strengths and limitations of this technology were identified and discussed.