The issue of slope stability is an core concern to geotechnical engineers. Traditional methods of analysis assume that the soil is fully saturated. However, throughout much of the world, slopes exist in residual soil deposits. Such soils are often unsaturated, and it has become clear that the traditional saturaded approach to assessing these slopes is inadequate. Current knowledge of the inflitration processes into unsaturated soil slopes is inadequate to enable reliable assessment of stability. This thesis constitutes an investigation into these inflitration processes, using numerical modelling techniques.