The translation of small molecule chemistries into efficient methodologies for polymer functionalization spans several decades, enabling critical advances in soft matter materials synthesis with tailored and adaptive property profiles. The present Perspective explores—based on selected examples—50 years of innovation in polymer functionalization chemistries. These span a diverse set of chemistries based on activated esters, thiol–ene/yne processes, nucleophilic systems based on isocyanates, reactions driven by the formation of imines and oximes, ring-opening processes, cycloadditions, and—in a recent renaissance—multicomponent reactions. In addition, a wide variety of chain types and architectures have been modified based on the above chemistries, often with exquisite chemical control, highlighted by key examples. We conclude our journey through polymer functionalization with the—in our view—most critically required advances that have the potential to move from “science fiction” to “science fact”.