  Some old and new evidence for the existence of the string (planar random
surfaces) representation of multicolour QCD are reviewed. They concern the
random surface representation of the strong coupling expansion in lattice
multicolour gauge theory in any dimension. Our old idea of modified strong
coupling expansion in terms of planar random surfaces, valid for the physical
weak coupling phase of the four-dimensional QCD, is explained in detail. Some
checks of the validity of this expansion are proposed. (The lectures given in
the Trieste Spring School and Workshop-1993 on String Theory).
