The two-dimensional polymerization and reaction at the solid/liquid interface has caused considerable attention in recent years because of its fundamental importance and many potential applications. Scanning tunneling microscopy (STM) provides the possibility for the observation and manipulation of polymerization and reaction occurring at the solid/liquid interface at the atomic level. Two-dimensional polymerization and reaction could be induced by external stimuli, such as electrochemistry-induced, STM tip-induced, or light-induced. The polymerization at the solid/liquid interface is the focus of this review, including the mechanism of polymerization and characterization of structural and electrical properties of the resulting polymers. Finally, the outlooks for developments in this field are described.