Special relativity theory is generalized to two or more ``maximal'' signalling speeds. This framework is discussed in three contexts: (i) as a scenario for superluminal signalling and motion, (ii) as the possibility of two or more ``light'' cones due to the a ``birefringent'' vaccum, and (iii) as a further extension of conventionality beyond synchrony.

14 pages with 3 figures, Latex, Talk given at the workshop Superluminal (?) Velocities, Cologne, June6-10, 1998. Revised version