This project investigates the performance of passive evaporative cooling towers in terms of cooling capacity, with the study focusing on understanding the geometric features that lead to high performance. Given the coupling of the governing equations and the lack of data available at low matrix Reynolds numbers, the performance is investigated from both a theoretical and experimental perspective. A model of the evaporative cooling tower is introduced and the governing equations are developed. An experimental program is formulated and a multivariable factorial analysis is used to investigate performance over a range of the independent variables. Established dimensionless parameters are used to investigate the heat and mass transfer in the matrix and correlations for the heat and mass transfer at low Reynolds number are derived from experimental measurements. The pressure loss in the system is investigated and it is shown that at low Reynolds numbers the pressure loss in the matrix is insignificant in comparison with the loss due to friction in the tower. It is also shown that the geometry of the tower significantly impacts on performance, with the tower height, diameter and matrix frontal area being significant v parameters. A figure of merit is introduced that allows the performance of towers to be compared. Through controlled experiments, the significant transient effects of wind, feedwater flow rate, and tower outlet geometry variation are investigated. It is shown that wind may significantly affect performance if not managed appropriately. It is also demonstrated that varying the feedwater flow rate or the geometry of the tower outlet may influence the performance of a tower.