Colour-Singlet Exchange in ep Interactions

Results presented at the DIS97 workshop by the H1, ZEUS and E665 collaborations on processes yielding large rapidity gaps and energetic leading baryons are reviewed. A consistent picture begins to emerge in which diffractive processes dominate when the fractional longitudinal momentum loss at the baryon vertex $\xpom$ is small, with substantial contributions from other processes as $\xpom$ increases. The diffractive mechanism in the deep-inelastic regime is found, both from inclusive measurements and final state studies, to involve the exchange of a gluon carrying a large fraction of the exchange momentum. Vector meson results show the transition from soft to hard production mechanisms with increasing precision.