Well testing and well hydraulics play a major role in applied hydrogeology. While well hydraulics aims at modeling the groundwater behavior in response to a perturbation -such as pumping -in a well, well testing aims at using these models in an inverse approach to infer the properties of the aquifer or of the well itself. The history of well hydraulics and well testing started in 1863 with Dupuit, who developed the first analytical solution to model radial flow to a well in steady state. In 1935, Theis published the most important analytical solution. The Theis solution assumes that the aquifer is confined, bidimensional, homogeneous, and isotropic. Subsequently, numerous models have been developed with the aim to enlarge the domain of applications. This article presents a brief review of these various models and describes their behavior in terms of drawdown and log derivative of the drawdown. The log derivative is used as a tool to help in the identification of the most appropriate model when analyzing field data.Encyclopedia of Hydrological Sciences. Edited by M G Anderson.