Enterprise systems are comprehensive and complex applications that form the core business operating system for many companies worldwide and throughout most industries. The selection, implementation, use and continuous change and evolution of enterprise systems (ES) require a great amount of knowledge and experience. Empirical studies show that the management of knowledge is one of the main cost drivers of Enterprise Systems projects. Consequently, organizations have realized the need to better leverage their knowledge management for Enterprise Systems. This chapter proposes a framework for structuring knowledge for Enterprise Systems. This three-dimensional framework is derived from meta-case studies and comprehensive literature analysis. It consists of dimensions for the ES life cycle, the Knowledge Management life cycle and the types of knowledge. Preliminary empirical insights show that especially the lack of soft knowledge is a critical success factor that leads to significant consulting costs in ES projects.