  We review the principle and methodology of leakage radiation microscopy (LRM)
applied to surface plasmon polaritons (SPPs). Therefore we first analyse in
detail the electromagnetic theory of leaky SPP waves. We show that LRM is a
versatile optical far-field method allowing direct quantitative imaging and
analysis of SPP propagation on thin metal films. We illustrate the LRM
potentiality by analyzing the propagation of SPP waves interacting with several
two dimensional plasmonic devices realized and studied in the recent years.
