  We establish a direct link between massive Ising model and arbitrary massive
$N=2$ supersymmetric QFT's in two dimensions. This explains why the equations
which appear in the computation of spin-correlations in the non-critical Ising
model are the same as those describing the geometry of vacua in $N=2$ theories.
The tau-function appearing in the Ising model (i.e., the spin correlation
function) is reinterpreted in the $N=2$ context as a new `index'. In special
cases this new index is related to Ray-Singer analytic torsion, and can be
viewed as a generalization of that to loop space of K\"ahler manifolds.
