▪ Abstract  The use of low-energy electron microscopy (LEEM) to study reversible surface phase transitions is reviewed. Representative experiments are described that highlight the key advantages of LEEM: the ability to image surfaces in situ, at elevated temperature, with good spatial and temporal resolution. With these capabilities, the evolution of individual surface features—domains, facets, islands, steps, etc.—can be measured. Real-time and real-space imaging make LEEM a powerful tool for characterizing the thermodynamics and kinetics that govern surface phase transformations.