Enterprise Systems (synonym: Enterprise Resource Planning systems) are customizable business operating systems that support the core processes and the main administrative areas of various industries in an integrated way. Selecting, implementing, using and continuously changing Enterprise Systems (ES) requires a great amount of knowledge and experience. The lack of inhouse ES knowledge and the high costs of engaging experienced implementation consultants have led organizations to realize the need to better leverage their knowledge resources. As the necessary knowledge is comprehensive, different kinds of expertise are required at different points in time during an ES project. This paper proposes a framework which structures the knowledge required to manage Enterprise Systems. This framework is derived from a comprehensive literature analysis and is applicable to organizations seeking to identify the relevant knowledge and to manage the knowledge resources. Based on the framework, this paper suggests how knowledge can be modeled in the ES context in order to identify the relevant knowledge during different stages of an ES project.