The thesis consists of a collection of papers appraising the role and design of waste stabilisation ponds (WSPs) in continental climates. It examines some of the underlying principles necessary to understand how these systems work, using laboratory experiments and mathematical modelling techniques. The state of the art of cold and continental climate ponds is reviewed with descriptions of pond types and operating modes, conventions used in process design, special aspects of construction, and a background into the microbiology and pathogen removal. A simple model based on first-order kinetics was developed to predict water availability, biochemical oxygen demand (BOD) and faecal coliform removal for intermittent discharge WSPs with different configurations and operating regimes. The results suggest a significant proportion of inflow could be saved for reuse by modifying pond design to suit climatic conditions. Three case studies of how this could be achieved are presented based on ponds in Kazakhstan. The model is used to consider some alternative design and operating protocols, using average and long-term climate records for cities across central Asia. Annual variability in climate parameters has a considerable effect, in particle on the date at which treated wastewater meets standards for discharge or re-use. The model was checked against a small number of datasets from WSPs subject to ice cover for part of the year, using local climate data. Good agreement was shown in predicting effluent BOD, particularly during spring and summer, and sensitivity analysis revealed some key parameters influencing performance. The model offers a powerful tool for simulating the cyclic behaviour seen in continental climate ponds with sufficient accuracy to permit tailoring of the design to local climatic conditions at specific sites. This allowed the production of contour maps covering a large part of central Asia and western China, showing predicted earliest discharge date, required area of maturation pond, salinity, number of months when discharge is not possible, and the ratio between pond inflow and outflow. The overall conclusion was that there is considerable scope for improvement in design methods for continental climate WSPs, although monitoring of full-scale systems is needed to provide verification and calibration data.