Multi-level modeling (MLM) as part of object-oriented modeling aims at fully utilizing the expressive power ofmultiple abstraction levels. While these levels where initially used to define domain-specific modeling languages, i.e. for linguistic purposes, the MLM community has long argued that there ismuch more to gain by tapping into ontological abstraction levels. While MLM is a rather specialized research field, there are now quite a number of different proposals. There is thus anopportunity to develop a uniform core of MLM that then possibly can become part of a standard and be taken up by the larger modeling community.