  The reported anomaly in deep-inelastic scattering at HERA has revived
interest in the phenomenology of R-parity violation. From the theoretical point
of view, the existence of R-violating interactions poses two considerable
problems. The first one concerns the flavour structure of the interactions and
the origin of an appropriate suppression of flavour-changing neutral-current
processes and lepton-family transitions. The second one concerns the way of
embedding R-violating interactions in a grand unified theory (GUT) without
introducing unacceptable nucleon decay rates. We show that the second problem
can be solved by a mechanism which is purely group theoretical and does not
rely on details of the flavour theory. We construct explicit GUT models in
which our mechanism can be realized.
