Polymer nanocomposites (nanoparticles integrated into a polymer matrix) have been recognized as a transformative category of materials in the domains of 3D and 4D printing, thereby facilitating novel avenues for advanced manufacturing and functional applications. The integration of nanoparticles within polymer matrices enhances mechanical strength, thermal durability, electrical conductivity, and functional responsiveness, thereby enabling the fabrication of high-performance components with tailored attributes. Nanopolymers have significantly improved printability in 3D printing, surface resolution, and structural integrity, rendering them applicable in sectors such as aerospace, biomedical devices, and electronics. In the swiftly evolving domain of 4D printing, nanopolymer composites facilitate dynamic, stimulus-responsive modifications in printed entities that are activated by external stimuli including heat, light, or moisture. This versatility encourages the creation of intelligent materials that may find use in deployable infrastructure, self-repairing systems, and soft robotics. This chapter provides an overview of nanoparticles for 3D and 4D printing. The structural, biological, and aeronautical applications of nano polymers are also discussed.