Paratransit operations in cities in developing countries play an important role in public transport provision. The operations are run within the realm of the infonnal sector and are highly flexible. There are numerous operators running one or two vehicles on a cash basis. This and other issues contribute to the problems with the services that are provided. Poor reliability and stability in supply are the main problems. Despite these serious problems, there has been little research on possible solutions to resolve them. The present study is aimed at improving understanding of the operation of such systems. It assesses the effects on users and operators of different routing, stopping and scheduling regimes. A new model of paratransit operations is developed. The problem of paratransit operations is conceptualised in terms of interactions between demand and supply. The interactions take place in time and geographical space and are shaped by the actions taken by individual users and individual vehicle operators. The model is designed to overcome some of the restrictions on the definitions of time - and in particular space - that are found in existing methodologies. A modelling approach designed to represent the two dimensions as realistically as possible was adopted. Two techniques are central to the construction of the model. Simulation techniques are used to model the temporal processes and a Geographical Information System (GIS) for the spatial processes. The two are complementary to overcome the inherent weaknesses in either approach. Modules are developed to represent demand and supply at a microscopic level. The Model of Paratransit Services (MOPS) involves interfacing a GIS and external modules for dynamic processes. The model was validated against field data collected in Harare, Zimbabwe. Experiments were run for a case study area and the results that were obtained on routing, stopping and scheduling regimes are reported in developing countries.