In this paper we discuss the application of scanning tunneling microscopy (STM) to probe the spatial distribution of surface reactions with atomic resolution. Scanning tunneling spectroscopy (STS) allows us to probe the valence electronic structure of an individual surface site and relate it to its reactivity. As an example we discuss a study of the initial stages of Si(111)‐7×7. We show that the mechanism of the reaction can be determined on the basis of STM and STS measurements. We then show that the STM can also be used to induce chemistry on the atomic scale. As examples we use desorption processes involving individual adsorbates on Si or involving substrate atoms.