As people and businesses experience the advantages and capabilities enabled by increased connectivity and integration between computer systems, a higher demand arises for the functionality and services that systems must provide. This necessitates the creation of a type of highly complex systems that themselves contain systems, which have a high degree of interconnectivity and interactions between them. This type of system is known as a System of Systems, which denotes a system that itself contains a group of heterogeneous constituent systems that via the interactions between them create a synergistic collaboration through which a higher common goal can be achieved. The development of a System of Systems is challenged by a high degree of complexity in the form of diverse stakeholders, geographical distributed development, a constant system evolution, an unpredictable emergence of behaviour, and the heterogeneity between the constituent systems. These challenges are being addressed in the field of Systems of Systems Engineering. The methodologies and tools used for analysis and development are however still in their infancy. This dissertation is focused on strengthening the Systems of Systems Engineering field by using a combination of Software Engineering and Systems Engineering, specifically with a focus on formal model based engineering techniques and tool-support hereof. The dissertation has three focus areas: managing integration challenges, enhancing the capabilities of System of Systems modelling and enabling collaborative development in formal modelling. The result is: a range of classification dimensions that characterise System of Systems; a System of Systems classification for design patterns; and multiple approaches for improving the tool-support for formal modelling techniques in System of Systems Engineering. vii There are a number of people who have been important in the completion of this dissertation, as their support, guidance and assistance made it all possible. To all of these, and many others, who contributed academically or personally, I owe a great deal. First I want to thank my supervisor Professor Peter Gorm Larsen from the Department of Engineering, Aarhus University. He has had a remarkable impact on both my research and my personal development. I am highly thankful for all he has taught me, both consciously and unconsciously, through his guidance, time and ideas. His never ending support and enthusiasm is both contagious and motivational. I want to acknowledge my colleagues in the COMPASS project whom have contributed strongly to my research by providing a foundation on which the research could be performed. They have contributed to my research with valuable ideas and feedback, for which I owe them my strongest appreciation. I also owe a strong recognition and thank you to Kenneth Lausdahl and Nick Battle for they support and work with the tool development efforts. Their impressive technical insights and expertises have been invaluable in the technical aspects of this dissertation. I wan...