The MMT Language. We introduce the MMT language, which provides a simple and scalable Module system for the development of Mathematical Theories. MMT permits to encode mathematical knowledge in a logic-neutral representation format that can represent the meta-theoretic foundations of mathematical and logical systems together with the represented knowledge itself and interlink the foundations at the meta-logical level. This ”logics-as-theories” approach makes system behaviors as well as their represented knowledge interoperable and thus comparable. Furthermore, MMT defines logic-independent notions of well-formedness and equivalence of modular mathematical theories. Thus, it provides an interface layer between formally rigorous mathematical systems, and knowledge management services which are not aware of the semantics of the processed knowledge