Abstract: Fluorescence microscopy offers chemists the ability to obtain subensemble information about synthetic reactions that would otherwise be obscured by the ensemble-averaging effects inherent to traditional analytical techniques. An important subset of studies that are possible through fluorescence microscopy is the investigation of polymerization reactions. These reactions have been key to produce items such as plastic bottles, electronic devices, resins, and clothing. The body of research presented in this dissertation pushes the boundaries for polymerization as investigated by fluorescence microscopy. These studies represent early examples of measuring catalytic selectivity at the single-molecule level, measuring single polymer-particle growth kinetics in solution, and obtaining physical-property information about polymers through FLIM. Polymer architecture is becoming increasingly complex, thus the development of novel and useful methods to characterize polymers, as described herein, is key to enable the development of next-generation polymeric materials.