Plant layout involves the spatial arrangement of equipment within the steel structure or building of a pint and considers the inter-connections through pipes and ducts as well as walks and vehicle transportation. An optimal layout has to ensure operability, adequete safety and an economic design. Therefore it is influenced by a whole range of factors such as process needs,maintenance, operational requirements, safety considerations and the available site. The resulting parameters differ significantly and compete with one another. Moreover, the conventional sequential work now of layout and detail engineering does not allow improvements of the layout at a late state of the project Today commercial CAD-systems are used as design tools for plant layout and detail engineering, but they do-not support planning and optimization of the layout. These decisions still need to be made by experienced senior engineers and designers.At the University of Dortmund new methods and software tools have been developed for conceptual plant layout. They are based on heuristic rules, statistical data and new algorithms for the spatial arrangement of equipment as well as pipe routing. The layout is calculated on the basis of process flow diagrams, process conditions, equipment design and further constraints related to the project Any change in these constraints alters the layout. Since the pipe routing is also calculated for a given layout, it becomes possible to identify areas where the layout or specific pipes should be changed in order to arrive at the most economic design.