Multi-Loop Calculations, Quark Masses and the Strong Coupling Constant

The impact of multi-loop calculations on precise determinations of charm- and bottom-quark masses and the strong coupling constant is discussed. Recent N3LO calculations, combined with new precision data, lead to a significant reduction of the errors. The results of these analyses, mc(3 GeV) = 0.986(13) GeV, mb(10 GeV) = 3.609(19) GeV and αs(MZ) = 0.1198(15) constitute the most precise and presently only N3LO determinations of these fundamental quantities.