Panayotaros P. A diagrammatic interpretation of classical and semiclassical perturbation theory (185K, TeX) ABSTRACT. We present a diagrammatic interpretation of the Lie-series classical perturbation theory and indicate the use of diagrams in a normal form calculation from fluid mechanics. We also extend the diagrammatic interpretation to the Rayleigh-Schr\"odinger perturbation theory of quantum mechanics. An advantage of the unified approach is that we have systematic expansions in $ \hbar $, so that in the $ \hbar \rightarrow 0 $ limit we easily recover the classical diagrams.