As the Model Driven Development (MDD) and Product Line Engineering (PLE) appear as major trends for reducing software development complexity and costs, an important missing stone becomes more visible: there is no standard and reusable assets for packaging the know-how and artifacts required when applied these approaches. To overcome this limit, we introduce in this paper the notion of MDA Component, i.e., a packaging unit for encapsulating business know-how and required resources in order to support specific operations on a certain kind of model. The aim of this work is to provide a standard way for representing this know-how packaging units. This is done by introducing a two-layer MOF-compliant metamodel. Whilst the first layer focuses on the definition of the structure and contents of the MDA Component, the second layer introduces a language independent way for describing its behavior. For a full specification, both layers can be merged using the UML2.0 package merge facility.