Multi-level modeling (MLM) represents a significant extension to the traditional two-level object-oriented paradigm with the potential to dramatically improve upon the utility, reliability and complexity of models. Different from conventional approaches, theyallow for an arbitrary number of classification levels and introduce other concepts that foster expressiveness, reuse and adaptability. A key aspect of the MLM paradigm is the use of entities that are simultaneously types and instances, a feature which has consequences for conceptual modeling, language engineering and for the development of model-based software systems.