[en] Intense laser beams may be backscattered from the converging electron beams of a linear collider to give a significant fraction of the luminosity in γγ or eγ collisions at close to the full machine energy. The design of the intersection region poses special problems, but an important programme of physics could be done with such a machine, especially if the Higgs boson mass is below 350 GeV/c². This review of the techniques and the physics draws on a number of recent workshops. Decisions will have to be made about whether the γγ and eγ options should be designed into an e⁺e^- collider from the beginning or added later. (orig.)