The ability to probe individual atoms and molecules have made it possible to reveal properties which otherwise would be hidden in the study of an ensemble of atoms and molecules. The scanning tunneling microscope (STM) with its unmatched spatial resolution and versatility literally allows us to touch atoms and molecules one at a time and to carry out experiments which previously were only imagined. One of the great attributes of the STM is that it provides a real space view of the individual molecules and the atomic landscape of their environment, thus removing many of the uncertainties surrounding the nature of the system under study. Combining its imaging, manipulation, spectroscopic characterization, and chemical modification capabilities, the STM has enabled direct visualization of chemistry by revealing the fundamental properties of atoms and molecules and their interactions with each other and the environment. While femtosecond lasers have made it possible to study chemistry at the temporal limit, the STM provides an understanding of chemistry at the spatial limit.