Within this project, the formalism ML-DEVS for explicitly describing multi-level models has been already developed. A modeling study on RNA structure folding revealed that it is possible to describe cell-biological and molecular systems with ML-DEVS. However, it also turned out that the language concept which is based on the metaphor of reactive systems with asynchronous communication patterns hampers modeling of biochemical reactions. Therefore, the goal of this project is to incorporate the previously achieved results for multi-level modeling - including those results gained by Mathias John - into a formal language with well-defined syntax and semantics. Thereby, the syntax shall be defnined in an intuitive way, so that the language can be easily learned by domain experts from biology. A rule-based approach following the paradigm of chemical reaction definitions seems to be promising. Furthermore, the syntax shall explicitly support the description of hierarchical model structures and interactions between different levels. The semantics shall follow the well-established concept of continuous time Markov chains. To examine the applicability of the formal language concept for cellbiological systems, the project shall further include a detailed modeling study.