This Ph.D. thesis studies issues in the area of construction informatics. Construction informatics is the theoretical study of formal and conceptual aspects in the domain of civil engineering and design. The thesis is a collection of papers which each treat a specific subject within domain analysis and conceptual modelling of civil engineering and design. Due to the interdisciplinary content, the first half of the study has been carried out at Department of Civil Engineering (BYG"DTU), The Technical University of Denmark; whereas the second half has been carried out at Informatics and Mathematical Modelling, The Technical University of Denmark. Supervisors have been Prof. Dines Bjørner (IMM) and Per Galle (BYG"DTU). The idea was to initiate the study at a place where engineering issues are discussed on a daily basis, and where the practical and theoretical knowledge of the domain is present. With origin in civil engineering and design issues, the study was directed towards computer science oriented theories in an attempt to introduce such theories in modelling and clarification of the domain. This strategy turned out to be a strength for the study and this thesis. However, it also discovered some problems in carrying out such a truly interdisciplinary Ph.D. study. Per Galle s and Dines Bjørner's common background in computer science has been essential for the success of this study. The original title of the Ph.D. project was Design and application of a civil engineering ontology. However, it became clear that there were going to be two main streams in the thesis, and that an actual monograph was not an appropriate format for the thesis. The main streams are both rooted in civil engineering ontology, and they are bound together by the overall issue of how civil engineering concepts relate. The issues of the thesis are treated from three angles: from computer science, from civil engineering and design theory, and from philosophy. It is characteristic for the thesis that these angles are all present in analysis and argumentation. The philosophical aspect is a natural ingredient as construction informatics primarily concerns the fundamental conceptual structures, and how models of these relate to engineering and design practice and reality. The aspect of design has been given high priority because this subject concerns the relation between representation and artefacts - a subject which is also essential in computer science, and which is deeply rooted in philosophy.