The broad theme of this thesis is engineering decision-making. The various factors that shape technological development are investigated using the development of Sydney's sewerage system as a case study. The thesis focuses on various key decisions, past and present, including the choice of water-carriage technology for sewage collection, the selection of sewage treatment technologies, and on-going preference of engineers and bureaucrats for ocean disposal. Also covered are the legislative and regulatory mechanisms, the policies of the Sydney Water Board with regard to industrial waste disposal and the relationship between the Board and the public. A study was made of historical documents, engineering reports and papers, parliamentary debates, annual reports, minutes, newspaper reports and secondary sources and personal interviews were conducted. Various bodies of literature were referred to and used, including the books and articles on the history and sociology of engineers, the politics of expertise and public participation and the emerging discipline of science and technology studies. It is concluded that the development of Sydney's sewerage system has been shaped by social, political and economic factors and that engineers have played a pivotal role in the decisions made through their deliberate shaping of knowledge and the performance of predictions they have made for various options. The decisions made in this way have been defended against public opinion and public participation in the decision-making process has been kept to a minimum. This thesis supports the argument that technology is socially constructed, that the technical cannot be separated from the social, and that an interactive model of technological development is more appropriate than a linear, causal one. It shows that the role of power in the shaping of technology is crucial, and in particular the alliance of state and professional power that occurs in the shaping of public sector technology.