  In this article we examine the compatibility of some recent results, results
relating M-Theory to String Theory, with the string-string duality conjecture
in six-dimensions. In particular, we rederive the relation between M-Theory and
Type IIA strings. We then go on to examine in detail M-Theory on $K3 \times
S^{1}$ and its relation to the Heterotic theory on $T^{4}$. We conclude with
some remarks on M-Theory on $T^{4}\times (S^{1}/{\bf Z}_{2})$ and its relation
to the Type II theory on $K3$.
