In situ transmission electron microscopy (TEM) permits the visualization of dynamic processes in materials, yet many processes propagate at rates far exceeding the temporal resolution of thermionic- or field emission-based TEMs. The dynamic transmission electron microscope (DTEM) is a photo-emission TEM capable of nanosecond-scale time-resolved imaging and diffraction. This talk will provide an introduction to the technique and then describe the application of DTEM to study the kinetics of crystallization of amorphous chalcogenide-based phase change materials, which are used for optical and resistance-based memory.