  We show that finite size scaling techniques can be employed to study the
glass transition. Our results follow from the postulate of a diverging
correlation length at the glass transition whose physical manifestation is the
presence of dynamical heterogeneities. We introduce a parameter B(T,L) whose
temperature, T, and system size, L, dependences permit a precise location of
the glass transition. We discuss the finite size scaling behaviour of a
diverging susceptibility \chi(L,T). These new techniques are successfully used
to study two lattice models. The analysis straightforwardly applies to any
glass-forming system.
