Nanoparticle-reinforced polymer composites (NpRPCs) exhibit desirable physical and chemical properties that include low density coupled with directed high stiffness and strength, optimal dimensional stability, superior temperature and chemical resistance, as well as relatively cost-efficient processing. These advanced composite materials have broad applications in the aircraft, aerospace, automobile, and sporting equipment sectors. Inventing new processing techniques and applying currently available approaches to fabricate novel material systems allow for bridging the nanoscale features of fillers to microscale structures and eventual extension to the macroscale composite properties for producing usable devices. Precise control of processing factors including (i) preserving intact nanoparticle geometries, (ii) uniform dispersion of the nanoparticles in polymers, (iii) effective matrix-filler interfacial interactions at molecular level, and (iv) alignment/orientation of the nanoparticle and/or polymer chains all can contribute to the superior properties of the composites. Discussions of such processing-structure relationship will be the focus of this talk. In particular, both thermoplastic and thermoset polymers have been used for fabrication of composite fibers and films. In addition, detailed exploration regarding the manufactured microstructure using experimental and simulation methods is conducted to fundamentally understand the microstructure-performance relationship in these polymer-based composite systems. These fundamental results will also be discussed as they pertain to improving composite fabrication and performances.