The articles in this issue of MRS Bulletin provide a sample of what is novel and unique in the field of in situ transmission electron microscopy (TEM). The advent of improved cameras and continued developments in electron optics and stage designs have enabled scientists and engineers to enhance the capabilities of previous TEM analyses. Currently, novel in situ experiments observe and record the behavior of materials in various heating, cooling, straining, or growth environments. In situ TEM techniques are invaluable for understanding and characterizing dynamic microstructural changes. They can validate static TEM experiments and inspire new experimental approaches and new theories.