String theories with (N, N') local world-sheet supersymmetries are rel
ated to each other by marginal deformations. This connects N = 1 and N
= 0 theories in which the target spaces are interpreted as space-time
s, N = 2 theories in which the target spaces can be interpreted as wor
ld-volumes, and theories with N greater than or equal to 3, in which t
he central charge vanishes - theories with zero target-space dimension
s. (C) 1997 Published by Elsevier Science B.V.