© Springer International Publishing AG, part of Springer Nature 2018. All rights are reserved. The increased commercial availability and the reduced prices of nanoparticles are leading to their incorporation in polymers and structural adhesives. This chapter outlines the principal types of nanoparticles, and the methods that may be used to disperse the particles in a polymer matrix. It discusses how nanoparticles can alter the mechanical properties (e.g., stiffness), electrical properties (e.g., conductivity), functional properties (e.g., permeability, glass transition temperature), and fracture performance of thermoset polymers. The effect of nanoparticles on joint performance is also discussed.