This chapter provides an extensive survey on the modelling and optimisation of DH networks and their recent advances. The hydraulic and thermal balance equations are presented. A hydraulic resistance identification method for pipes, based on pressures and flow rates recorded at the heat source and heating substations, is described to accurately determine the distribution of pressure and flow rates in nodes. The primary methods of hydraulic analysis and numerical algorithms for solving them are presented, including the node method in conjunction with the Newton–Raphson algorithm for steady-state hydraulic modelling of DH networks and the characteristic line method for solving the hydraulic transient distributed parameter model of these networks. A quasi-dynamic hydrothermal model that employs the lumped capacitance method to calculate heat losses in pipes and is solved using the finite volume method is included to estimate temperatures, pressures, and mass-flow rates within the network. A single- and multi-objective optimisation problem is generally formulated, and the main objectives, decision variables and constraints for the design and operation of heat distribution networks are synthesised and discussed. The main deterministic and heuristic optimisation techniques for DH networks are briefly explained and classified, with a focus on their optimal design. The fields of application of the main simulation tools are also briefly described. Additionally, some deterministic and heuristic single- and multi-objective optimisation models for DH network design are included and numerically exemplified. The state-of-the-art DH network optimisation has also been reviewed, and the optimisation models are classified into different categories depending on the problem type and the adopted optimisation technique. Finally, the advantages and disadvantages of the optimisation methods employed in this area are included, along with some recommendations on future research directions.