  This review provides a broad overview of the studies and effects of nonlocal
response in metallic nanostructures. In particular, we thoroughly present the
nonlocal hydrodynamic model and the recently introduced generalized nonlocal
optical response (GNOR) model. The influence of nonlocal response on plasmonic
excitations is studied in key metallic geometries, such as spheres and dimers,
and we derive new consequences due to the GNOR model. Finally, we propose
several trajectories for future work on nonlocal response, including
experimental setups that may unveil further effects of nonlocal response.
