  Experimental discovery of the dilaton would provide strong evidence for
string theory. A light dilaton could show up in current tests of the inverse
square law for gravity at sub-millimeter distances. In the large extra
dimension scenario, Kaluza-Klein excitations of the dilaton can also contribute
to the cooling of supernovae. In order to quantify these effects we compute the
couplings of a low energy dilaton to matter. These predominantly arise from the
fundamental dilaton coupling to the gluon field strength, which receives a
sizable enhancement from QCD scaling. We show that detection of the dilaton
will give a direct measurement of the QCD coupling constant at the string
scale. Particular attention is paid to the size of equivalence principle
violating dilaton couplings.
