On the surface of dielectric materials with the negative dielectric constant a resonance occurs. This resonance is called the surface plasmon resonance and is underlying physical phenomenon of important imaging modalities such as SERS (surface enhanced Raman spectroscopy). It turns out that the Plasmon resonance is closely related to the spectrum of the Neumann-Poincare (NP) operator defined on the surface. In this talk I will explain the connection of the plasmon resonance and the spectrum of the NP operator and review recent development in the spectral theory of the NP operator. The NP spectrum is also closely related to the anomalous localized resonance which attracts much attention in connection with the invisibility cloaking. I will explain this as well.