The paper presents the thermohydraulic models for aquifer thermal energy storage developed by the Lund Group for Ground Heat. The basic assumption is that the aquifer is horizontally homogeneous and that the groundwater flow is two-dimensional without a vertical component. The groundwater flow field is then given by an analytical function, or conformal transformation, which is obtained from the positions of the well, the pumping rates, and the regional flow.The first set of PC models concerns the groundwater flow and the motion of thermal fronts for any set of wells and a regional flow. The flow field, with streamlines and stagnation points, is presented graphically on the screen. The motion of the thermal fronts is determined by particle tracking. These interactive models have proven to be very convenient and useful design tools.The complete three-dimensional thermal process is solved in the second set of PC models. The groundwater flow is again given by the explicit analytical formulas, while the thermal process is solved numerically. The coupled groundwater and the heat flow process in the aquifer is dealt with using a new entropy-conservation technique.The models are carefully documented and available on PC. They have been validated against a few field experiments and they are used extensively for design studies.