We teach it to undergraduates [as I am doing today!] and claim that it captures many properties of elemental metals? Then we say it works badly for cuprates and other strongly correlated electron metals. But, just how good is it? Surely, this should be in textbooks. But, it actually took me a long time to find the graph below. It shows the frequency dependence of the real and imaginary part of the dielectric constant for gold. The solid lines are the Drude predictions with two free parameters, the dc conductivity and the quasi-particle scattering time. The experimental data covers the range 50 to 20,000 cm-1.Applied Optics paper by Ordal et al.