  Weakly Interacting Massive Particles (WIMPs, $\chi$) are candidates for Dark
Matter. WIMP searches at lepton colliders are complementary to searches at
hadron colliders and direct and indirect detection, since they directly probe
the coupling to electrons which a priori is independent of the coupling to
hadrons. Like at hadron colliders, WIMP pair production can be observed via an
additional tag particle, in particular a photon from initial state radiation
($e^+e^-\rightarrow\chi\chi\gamma$). With this technique WIMP masses to nearly
half the centre-of-mass energy can be probed. Polarised beams are essential to
reduce Standard Model backgrounds and to characterize the properties of the new
particles in case a signal is discovered. Prospects for a mono-photon WIMP
study at the International Linear Collider will be discussed in the context of
EFT. In addition, detector requirements will be presented.
