  Selectrons may be studied in both e-e- and e+e- collisions at future linear
colliders. Relative to e+e-, the e-e- mode benefits from negligible backgrounds
and \beta threshold behavior for identical selectron pair production, but
suffers from luminosity degradation and increased initial state radiation and
beamstrahlung. We include all of these effects and compare the potential for
selectron mass measurements in the two modes. The virtues of the e-e- collider
far outweigh its disadvantages. In particular, the selectron mass may be
measured to 100 MeV with a total integrated luminosity of 1 fb^-1, while more
than 100 fb^-1 is required in e+e- collisions for similar precision.
