Linear polymers, or thermoplastics, make up most single-use plastics, given their outstanding mechanical properties, including high strength and the ability to undergo extensive deformation before breaking. However, they cannot recover from the large plastic deformations. Network polymers, or thermosets, are ubiquitous in many applications, such as tires, fiber-reinforced composites, hydrogels and, coatings. Network polymers have covalently crosslinked three-dimensional structures that endow them with dimensional stability, resistance to heat and solvent, and the ability to recover from deformations (i.e., shapememory effect). Neat network polymers typically fall into two categories: rubbery network polymer, also known as elastomer, with a glass transition temperature (Tg) below ambient temperature, and glassy network polymer, with a Tg above ambient temperature. While elastomers can recover their original shape and material properties from large deformations (e.g., > 100% strain), glassy network polymers are notoriously brittle and typically fracture with <5% strain. Accordingly, ductility -a material's capability of sustaining plastic deformation under tensile stress before failure -has yet to be achieved in network polymers. We envision that achieving ductility in glassy network polymers will advance polymer science and materials by endowing plastics with many desirable attributes of network polymers, including elastic recovery from deformations.