The following chapter provides a design flow and scaling rules for overshot waterwheels. The design flow has three parts: the design of the geometric wheel size, the efficiency calculation and the parameters of construction of the drive system. A detailed description of the design process is given and two examples are calculated to show the application of the design flow. The second example is carried out as a short table design flow. Both overshot waterwheels of the examples were realized and show their good performance at the respective hydropower locations. In addition, the scaling rules of waterwheels are derived. These rules allow the reader to use model experiment results for large wheels. The application of such rules is illustrated for one specific overshot waterwheel.