I review the status of the modern theoretical approach to weak decays of
heavy flavor hadrons based on the 1/m_Q expansion in QCD. The qualitative
features are explained and the subtleties in simultaneously incorporating
perturbative and power-suppressed effects are addressed. A few topical
phenomenological applications are discussed in quantitative detail.Comment: 30 pages, 3 figures in the text; LaTeX. Talk given at the Symposium
on Radiative Corrections (CRAD96), Cracow, 1-5 August 1996. To appear in
Proceedings of "CRAD96
