Modern-day transmission electron microscopes show us the position and nature of the individual atoms within a material. But better still, we can record movies that show how atoms are rearranged during chemical reactions. This is especially relevant to energy-related materials, where energy storage is often accompanied by changes in atomic configuration; in microelectronics, where processing must create precisely defined nanostructures; in structural materials such as cement during hydration, and in quantum materials, where the details of atomic structure determine how well a qubit will work. Through these and other examples, I will show how time-resolved electron microscopy helps us develop new materials and optimize the performance of materials we already know.