Linear colliders offer unique opportunities to study gamma-gamma (gg), gamma-electron (ge) interactions. Using the laser backscattering method one can obtain gg, ge colliding beams with an energy and luminosity comparable to that in e+e- collisions. This work is a part of the Conceptual Design of TESLA/SBLC linear colliders describing a second interaction region for gg, ge collisions. We consider here possible physics in high energy gg, ge collisions, e -> g conversion, requirements to lasers, collision schemes, attainable luminosities, backgrounds, possible lasers, optics at the interaction region and other associated problems