  The electromagnetic properties of subwavelength metallic surfaces are due to
two kinds of elementary distinct waves, the famous surface plasmon polariton
and the quasi-cylindrical wave, which are both scattered by the subwavelength
indentations as they propagate on the metal. The ab-initio microscopic
description of the electromagnetic properties starting from the sole knowledge
of the elementary waves launched in between the indentation has a long history
in grating theories. We review the evolution of the ideas and the fundamental
principles that govern these waves and their impacts. For the sake of
illustration, the emblematic case of a metal surface perforated by a
subwavelength-hole array, which exhibits remarkable transmission properties, is
taken to illustrate our purpose.
