Dualities of type 0 strings

It is conjectured that the two closed bosonic string theories, type 0A and type 0B, correspond to certain supersymmetry breaking orbifold compactifica tions of M-theory. Various implications of this conjecture are discussed, i n particular the behaviour of the tachyon at strong coupling and the existe nce of non-perturbative fermionic states in type 0A. The latter are shown t o correspond to bound states of type 0A D-particles, thus providing further evidence for the conjecture. We also give a comprehensive description of t he various type 0 closed and open string theories.