The objective of groundwater resource investigation is to provide an efficient supply of water to the surface. The engineering design of the most efficient installations is covered by other texts and is not repeated. The loss of energy as water passes through the formation close to an abstraction well is frequently considerable and measurement of hydraulic head outside and inside the casing is required to identify this. In this Chapter, radial flow in the vicinity of the borehole is described and modelled. Theoretical results are compared with extensive physical tank models carried out in the past and the loss of laminar flow identified. Radial flow equations are also the basis of pumping test analysis and commonly used techniques are reviewed with examples of applications provided.