  We analyze nonlinear collective effects near surfaces of semi-infinite
periodic systems with multi-gap transmission spectra and introduce a novel
concept of multi-gap surface solitons as mutually trapped surface states with
the components associated with different spectral gaps. We find numerically
discrete surface modes in semi-infinite binary waveguide arrays which can
support simultaneously two types of discrete solitons, and analyze different
multi-gap states including the soliton-induced waveguides with the guided modes
from different gaps and composite vector solitons.
