In the two centuries since the discovery of δ Cephei and η Aquilae, the study of Cepheids, and of pulsating stars in general, has become a very important field in astronomy. The usefulness of Cepheids, both as distance indicators and as test objects for stellar astrophysics, has been amply demonstrated, and if one just looks at the flood of papers on Cepheids that appears each year, it is clear that the subject is not only old and respectable, but also still very much alive. This twohundredth anniversary is therefore an appropriate occasion to evaluate what we have learnt about Cepheids, and where the remaining problems lie.