  We establish a general map between Grassmann functionals for fermions and
probability or weight distributions for Ising spins. The equivalence between
the two formulations is based on identical transfer matrices and expectation
values of products of observables. The map preserves locality properties and
can be realized for arbitrary dimensions. We present a simple example where a
quantum field theory for free massless Dirac fermions in two-dimensional
Minkowski space is represented by an asymmetric Ising model on a euclidean
square lattice.
