  We calculate the cross sections for the single production of doubly-charged
dileptons, both scalar and vector, at $e^+e^-$, $e\gamma$ and $\gamma\gamma$
colliders at $\sqrt{s}=500$ GeV and 1 TeV. The $e\gamma$ mode is by far the
most promising -- dileptons whose coupling is as weak as
$O(10^{-4})\alpha_{em}$ can be observed, for masses virtually up to the
kinematic limit. Dileptons of mass up to $\sqrt{s}$ can also be seen in
$e^+e^-$ and $\gamma\gamma$ colliders, for couplings of order $\alpha_{em}$. In
all three colliders, most of the cross section comes from events in which the
only particles detected are $e^-e^-$, the decay products of the dilepton,
yielding an unmistakeable experimental signature.
