The efficient construction of large industrial plants (e.g. concrete plants, chemical plants) in high quality requires precise planning and execution of the individual logistics and assembly steps. For this purpose, detailed step-by-step instructions should be prepared that can be clearly interpreted and thus implemented by the staff on site carrying out the work. Especially meaningful and project-specific assembly instructions are very important. In some cases, digital plant models are already being used to visualize the assembly sequences. The individual steps of assembly are animated together with the associated plant elements, staff and other resources. However, the exact assembly sequence has to be specified by a production engineer. This paper presents an approach for semi-automatic generation of step-bystep instructions for assembly in large-scale plant construction. Basic information for the assembly of a plant can already be taken from digital (BIM) models (BIM: Building Information Modeling). They include, e.g., information on components, construction details and connections. Based on this information, specific assembly sequences can be defined as rules for various plant groups. These rules are collected in a central database and provided for further use. An example shows how individual assembly sequences can be generated based on a digital plant model using the rule set. The results can be made available as 4D animations to the involved employees on the construction site. The assembly sequences defined for a project can provide useful support for planning the processes on the construction site (assembly, transport and storage of building elements). A simulation provides the validation of the planning created for this project and therefore also the validation of the defined assembly processes.