We discuss the use of two QCD based effective field theories in determining parameters of the standard model. Heavy Quark Effective theory provides a framework for studying the weak decays of the B meson. We calculate the B → Xclv decay rate to second nonvanishing order in the HQET expansion and compare the theoretical prediction to experimental data. This allows us to determine the b and c pole quark masses and the weak mixing angle Vcb. Nonrelativistic QCD is an effective field theory in which bound states of two heavy quarks can be analyzed conveniently. We use this approach to compute the leading relativistic corrections to the decay of S-wave quarkonia. These corrections can be expressed in terms of the leading order result and the quark pole mass. Including color octet contributions and the first relativistic corrections, we extract the value of αs from low energy data. We also show that the color octet contributions to the decay rates are not negligible.