Scanning tunneling microscopy (STM) has revolutionized the fields of heterogeneous catalysis and environmental sciences by providing unique insights into the atomic-scale structure of model catalysts. For the first time, STM has revealed the structure of active sites, including steps, kinks, and special atomic geometries in compounds. It has provided images of atomic scale dynamic processes, including diffusion and reactions. STM can operate in environments of gases and liquids, as found in real life and in industrial processes. We illustrate these unique capabilities with examples and how the information obtained can lead to industrially relevant information and help the design of new catalysts.