M theory on orientifolds of K3 x S1.

We present several orientifolds of {ital M} theory on {ital K}{sub 3}{times}{ital S}{sup 1} by additional projections with respect to the finite Abelian automorphism groups of {ital K}{sub 3}. The resulting models correspond to anomaly-free theories in six dimensions. We construct explicit examples which can be interpreted as models with eight, four, two, and one vector multiples and {ital N}=1 supersymmetry in six dimensions. {copyright} {ital 1996 The American Physical Society.}