Information systems are more and more often based on aggregation of other systems that must be maintained and evolved in an agile way and without un- controlled entropy. This is not without interoperability problems! Among others, the aim of Model-Driven Engineering (MDE) is to provide solutions for interoperability issues between systems. This paper summarizes thoughts that have come up from the specific action "Interoperability of information systems and model-driven engineering: What challenges? What solutions?" supported by inforsid. We propose a summary of approaches that are based on MDE and knowledge engineering and that tackle in- teroperability issues in the industry. Open questions and limitations that raised during the meetings are also reported.