  Experiments at electron-positron colliders can search for dark matter
particle pair-production in association with a photon. We estimate the
sensitivity of this search at the proposed International Linear Collider (ILC),
under a variety of run scenarios. We employ the effective operator formalism to
provide a quasi-model-independent theoretical description of the signal, and
present the reach of the ILC in terms of the scale \Lambda suppressing the dark
matter-electron coupling operator. We find that at the 250 GeV center-of-mass
energy, the ILC can probe \Lambda up to 1-1.2 TeV, a factor of 2.5-3 above the
best current bounds from LEP-2. With 1 TeV energy and polarized beams, the
reach can be extended to 3-4 TeV. The ILC can discover this signature even if
annihilation to electrons provides only a small fraction of the total dark
matter annihilation rate in the early universe. We also argue that large
regions of parameter space allowed by current LHC and direct detection bounds
will be accessible at the ILC.
