Crosslinked polymers are an important class of polymer material that includes thermosetting resin, rubber (elastomer), and gel. In this chapter, the development of dynamic functions in crosslinked polymers aiming to improve the materials performance, particularly the mechanical properties, are reviewed. The main focus is on five dynamic functions: toughness, self-healing and self-recovery, malleability and moldability, self-strengthening, and shape memory. The key mechanisms that enable these dynamic functions—dynamic bonds and phase transitions—are discussed. Characterization techniques utilized for dynamic functional materials are also reviewed: techniques for molecular-level characteristics, hierarchical structure of polymers, and macroscopic mechanical properties are briefly explained. The rest of this chapter is dedicated to the introduction of some representative studies on dynamic functional crosslinked polymers. The examples are organized by the type of key mechanism (e.g., the dynamic bond type) for dynamic functions.