Enterprise Modeling (EM) has two main purposes: (1) Developing the business, which entails developing business vision, strategies, redesigning the way the business operates, developing the supporting information systems, etc., and (2) ensuring the quality of the business where the focus is on sharing the knowledge about the business, its vision and the way it operates, and ensuring the acceptance of business decisions through committing the stakeholders to the decisions made. In addition, EM has also shown to be useful as a general tool for articulating, discussing, and solving organizational problems. Based on a number of case studies, interviews and observations this chapter defines what is required from EM when adopted for these purposes and intentions respectively. More precisely, it addresses the following types of requirements; documents and models required as input, models that should be developed, requirements on the modeling language, requirements on the modeling process, tool requirements and model quality requirements. The defined requirements are then discussed taking a specific EM method, Enterprise Knowledge Development (EKD) as example.