Hydraulic simulation models are frequently used nowadays for the planning and operational management of water distribution systems. To be effectively used, these models need to be calibrated first. During the calibration process the unknown model parameter values are determined with the aim to achieve as best as possible match between the simulated model predictions and the corresponding measurements obtained in the field. Traditionally, calibration was, and, unfortunately, still is in some cases, treated as a manual task. However, as this book (based on the author''s PhD thesis) will show, better results can be achieved if calibration of the analysed hydraulic model is formulated and solved as an optimisation problem. In addition, the book addresses the related problem of sampling design for calibration which aims to determine what,