Most corporations conduct their business according to processes they developed over time. Making experiences the corporation will adapt their processes to reflect best practices. In software development the process of building programs might consist of phases like requirement analysis, implementation, tests and support. These need to be modeled and supported by a computer system. This diploma thesis will focus on long-term processes. In contrast to processes that complete in a matter of hours or less the former will most likely be adapted to customer requests, changes in circumstances or events that occur during execution. An introduction will illustrate problems and analyze available solutions. In a next step the concepts for a solution will be presented at an abstract level. The main part of this thesis contains an architectural overview of the Workflow Enactment Service. The implementation concepts enactment and adaptation will be presented. These include the model representing the business process, workflow elements, enactment, adaptation and persistence. In a conclusion the implemented prototype will be analyzed, problems and ideas for improvement stated.