Science: The ability to observe individual chemical reactions in real time is reshaping our understanding of molecular processes, revealing subtleties previously hidden in ensemble averages. For example, single-molecule fluorescence detection methods have revolutionized optical microscopy and in situ studies of chemical and biological systems. Liquid cell in situ transmission electron microscopy (TEM) is poised to write a new chapter in the solution synthesis and processing of materials. Haimei Zheng and colleagues use a TEM liquid cell that allows liquids to be examined within the vacuum environment of a TEM in an elegant experiment that uncovers dynamic processes in the growth of platinum (Pt) nanocrystals. Related LinkObservation of Single Colloidal Platinum Nanocrystal Growth Trajectories