Summary:The role of the environmental scanning electron microscope (ESEM) in the study of cement-based materials is reviewed. Since water is an intrinsic part of the microstructure of cement paste, techniques that facilitate the study of wet specimens are necessary. The evolution of techniques is traced from standard microscopic methods to the use of the ESEM for in situ analysis. The importance of past and current work is discussed, including novel analytical methods designed for the study of cement pastes. Directions for future work are also discussed.