This thesis deals with the formal foundation, conceptual design, and prototypical implementation of workflow management systems. Based on properties of information systems applications, research issues in workflow management and requirements of suitable workflow support are characterized. In particular, the need for flexibility and dynamic adaptations is identified, i.e., the ability of workflow management systems to adapt running workflow instances to changes in the environment of application processes. Re-use of workflow schemata, the integration of application objects as well as high scalability and availability are characterized as additional important properties of workflow management systems. As a formal foundation, a workflow language based on directed graphs is introduced, using a mathematical formalism. In this formalism, workflow schemas and workflow instances are described. Specific properties of workflow schemas like the prefix-closed property with respect to workflow schema consistency are formalized. Workflow application development processes are characterized as specific software processes, and a workflow design methodology is proposed. The conceptual design of workflow management systems is studied in some detail. After a brief characterization of the conceptual design and the architecture of a workflow management system, the potentials for improvements are identified. Goals for the conceptual design and prototypical implementation of a novel workflow management system are derived. Since a mathematical formalization is not sufficient as a basis for the conceptual design of a workflow management system, object-oriented design methods are used. Workflow schemas, workflow instances, and related artifacts are modeled as objects. Since the resulting class diagram specifies the structure of workflow-relevant objects, it amounts to a workflow meta schema. The workflow meta schema is designed to support dynamic adaptations of running workflow instances by changing the relationship of a workflow instance object to a workflow schema object. To control dynamic adaptations properly, correctness criteria using the mathematical formalization are introduced. Since workflow applications are typically performed in heterogeneous and distributed environments, a distributed object-oriented middleware is used as an implementation platform. Due to the object-oriented approach on the conceptual level, the system design and the implementation platform match nicely. A set of fundamental services are designed and implemented. The usage of the system is illustrated by a sample workflow application, which also introduces a workflow client application. The workflow client application can be configured to the requirements of different groups of persons involved in workflow applications.