This paper presents the results of the analysis of the fundamental assumptions of seven major schools of thought in IS development – software engineering, database management, management information systems, decision support systems, implementation research, the sociotechnical approach, and the infological approach. The analysis is based on a distinction between the ontology, epistemology, methodology and ethics of the research. Ontology, forming the major constituent, is decomposed into five dimensions based on the major objects of IS research: the view of information/data, the view of the information/data system, the view of human beings, the view of technology, and the view of organizations and society. While the results of the analysis indicate certain variations between schools, especially in their ontological assumptions, all seven schools have quite similar assumptions. These are dominated by the view of information/data as descriptive facts, an information system as a technical artefact with social implications, a view of technology as a matter of human choice, predominantly a structural view of organizations, postivistic epistemology, a means-end-oriented view of IS science, and values of IS research reflecting organizational and economic goals; and most of these also have user-oriented criteria. In the case of the view of human beings and research methods it is not possible to identify any clear, dominant views. These assumptions are largely consistent with each other and provide support for the alleged existence of an identifiable ‘orthodoxy’ in IS research.