  Electron energy-loss spectroscopy (EELS) offers a window to view nanoscale
properties and processes. When performed in a scanning transmission electron
microscope, EELS can simultaneously render images of nanoscale objects with
sub-nanometer spatial resolution and correlate them with spectroscopic
information of $\sim10 - 100$ meV spectral resolution. Consequently, EELS is a
near-perfect tool for understanding the optical and electronic properties of
individual and few-particle plasmonic metal nanoparticles assemblies, which are
significant in a wide range of fields. This review presents an overview of
basic plasmonics and EELS theory and highlights several recent noteworthy
experiments involving the electron-beam interrogation of plasmonic metal
nanoparticle systems.
