The understanding of nucleation and crystallisation mechanisms in glasses re- quires direct observations at the nanometric scale (corresponding to the size of the first crystalline seeds). Electron microscopies, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM), use an electron beam to obtain chemical and/or structural information. These techniques have been long used to observe the phase separation in glasses [222, 556] or microstruc- tures of glass-ceramics [387]. Recent advances in electron microscopy now offer opportunities to probe samples at nanometer scales (or even sub-nano) and to provide new information on the nucleation processes. In this chapter, we pre- sent the main options offered by electron microscopy, including the latest tech- niques, together with some examples of the use of these techniques expanding our knowledge of the nucleation phenomena.