e-Learning organizations are focusing heavily on learning content reusability. The ultimate goal is a learning object economy characterized by searchable digital libraries of reusable learning objects that can be exchanged and reused across various learning systems. To enable such approach, basic questions of learning content interoperability need to be addressed. This paper investigates the interoperation of learning content defined according to different specifications. A number of content models are reviewed that define learning objects and their components. Based on a comparative analysis, the content models are mapped to a generic model for learning objects in order to address interoperability questions and to enable share and reuse on a global scale.