The basis for the thesis is to assess the usefulness of describing and analysing transportation and logistics systems as being complex systems. The reason and assumption being that in the future more integrated and sophisticated systems and solutions will be demanded. The requirements of the future will also be the requirements of a sustainable society and this also requires higher sophistication in that industry and consumers demand faster and cheaper solutions, but with less environmental impact. The ultimate goal is to use complexity to meet the demand for more sophisticated approaches, models and methods both to better understand these systems and to be able to manage and control them in the most efficient way. In this thesis the concept of complexity is applied to the context of transportation and logistics system in order to better understand the characteristics of these systems. It is an unorthodox method within the research area of transportation and logistics, but it is argued that the concept of complexity provides a valid and valuable model for the analysis of transportation and logistics systems. Complexity is throughout the thesis treated as an important aspect of transportation and logistics systems, and is as a concept used to describe, analyse and model transportation and logistics systems and their properties. The concept of complexity as well as other related concepts are analysed and a conceptual model of transportation and logistics systems' complexity is developed. This model describes the complexity of transportation and logistics systems as residing primarily within three core properties: the network, the process and the stakeholder properties. These properties in their turn are influenced by other extended properties such as variety, connectivity, cognition etc. Three different perspectives; the network, the process and the stakeholder perspectives are used to describe and analyse the transportation and logistics systems. The network perspective focuses primarily on the structure of the transportation and logistics systems, while the process perspective focuses on the activities and dynamics and the stakeholder perspective focuses on the perceptions, represented by the different stakeholders. Four empirical studies are used as a base for the analysis and these four studies are representative for four different aspects of transportation and logistics systems; terminals, supply chains, distribution channels and the transportation of passengers. A measure of transportation and logistics' systems complexity is also develop and applied to these different systems. These studies provide an empirical basis for the research problem studied as well as a validation of the usefulness of the conceptual model of complexity and the proposed measure.