It was pointed out in Chapter 5 that the groundwater flow equation is dependent on the medium composition and the hydraulic gradient and that the continuity equation is universal and can be applied in any situation. So far in this book the groundwater flow was assumed to abide with the Darcy law which is valid for laminar (linear) flow types only. However, in practice, there appears many situations where its application is questionable. Nonlinear flow is seldom, if ever, considered in groundwater movement, except for flow in the immediate vicinity of pumped wells. Recently, an interest has arisen for evaluation of the aquifer parameters with nonlinear flow. It is the purpose of this chapter to give available pumping test analysis of nonlinear flow.