  We consider the possibility of neutron-antineutron ($n-\bar n$) conversion,
in which the change of a neutron into an antineutron is mediated by an external
source, as can occur in a scattering process. We develop the connections
between $n-{\bar n}$ conversion and $n-{\bar n}$ oscillation, in which a
neutron spontaneously tranforms into an antineutron, noting that if $n-{\bar
n}$ oscillation occurs in a theory with B-L violation, then $n-{\bar n}$
conversion can occur also. We show how an experimental limit on $n-{\bar n}$
conversion could connect concretely to a limit on $n-{\bar n}$ oscillation, and
vice versa, using effective field theory techniques and baryon matrix elements
computed in the M.I.T. bag model.
