The trematode Schistosoma haematobium, which causes urinary schistosomiasis in humans, is endemic to Unguja island, Zanzibar and the freshwater snail Bulinus globosus acts as the intermediate host in this setting. Hence the distribution and infectivity of these snails are directly implicated in control of the disease within the human population. In this thesis, a variety of different experiments were undertaken to assess various aspects of the transmission process encompassing S. haematobium levels in snail populations, miracidial choice patterns and development of molecular tools for assessing prepatent snail infection levels. The most effective tool for detecting S. haematobium within the snail host was Dra 1 peR assay. This assay can detect parasite DNA within susceptible and non-susceptible species of snail, with exposure to as little as a single miracidium and at 24 hours post exposure to the parasite. Patent and prepatent prevalence were determined over the course of four years in transmission sites and rate of infection was assessed by using sentinel snails. Prepatent prevalence of S. haematobium varied between 50 and 100% throughout the year. Sentinel snails were exposed to infection within a transmission site: after ,72 hours approximately a quarter of snails had been penetrated by the parasite. S. haematobium miracidia, in choice chamber experiments, showed a preference for B. globosus and Bulinus nasutus over the sympatric species, Cleopatraferruginea and Thiara scabra. High resolution IH NMR spectroscopy was able to differentiate between Bulinus species from Zanzibar and mainland Africa and between unexposed and exposed snails. Biomarkers for S. haematobium within human urine samples were not determined due to high levels of polyparasitism within the study group. These results demonstrate that while urinary schistosomiasis remains a debilitating and important disease on Zanzibar, a greater understanding of snail parasite dynamics will be critical in designing and implementing effective and sustainable control measures.