The postpolymerization modification of block copolymers has seen a growing interest in the past decade ranging from fundamental synthesis and structure property relationships to potential applications. The resulting side-chain-modified block copolymers can retain the properties inherent to the parent block copolymer core, while introducing side-chain functionality that can allow for a tunable handle on material properties and consequently applications. In this Perspective, we discuss different methods of postpolymerization side-chain modification of block copolymers using either covalent or noncovalent strategies. We also describe potential applications, discuss some of the challenges remaining in this area, and suggest strategies for the advancement of the field.