  Observations of rare processes containing large rapidity gaps at high energy
colliders may be exceptionally informative. However the cross sections of these
events are small in comparison with that for the inclusive processes since
there is a large probability that the gaps may be filled by secondary particles
arising from additional soft interactions or from gluon radiation. Here we
review the calculations of the probability that the gaps survive population by
particles from these effects for a wide range of different processes.
