Domain Specific Languages (DSLs) play a cornerstone role in Model-Driven Software Development for represent- ing models and metamodels. DSLs are usually defined in terms of their abstract and concrete syntax only. This al- lows the rapid and inexpensive development of DSLs and their associated tools (e.g., editors), but does not allow the representation of their behavioral semantics, something es- pecially important for model operations like simulation and verification. In this paper we explore the use of Maude as a formal notation for describing models and metamodels, including the specification of their dynamic behavior.