SOM is an object-oriented methodology for comprehensive and integrated modeling of business systems. It is based on a framework consisting of the layers business plan, business process model, and business application system as well as views on these layers focusing on specific aspects. This contribution presents the SOM language for business process modeling and shows how business application systems can be linked to business process models. The language uses concepts of systems theory and is based on the notions of business object, business transaction, task, event, and service. Business objects are coordinated by feedback control or by negotiation. Decomposition rules allow a stepwise refinement of a business process model. The contribution includes a detailed example to illustrate the methodology.