Multi-Paradigm Modelling (MPM) is a research field focused on solving the challenge of combining, coupling, and integrating rigorous models of some reality, at different levels of abstraction and views, using adequate modelling formalisms and semantic domains, with the goal to simulate (for optimization) or realize systems that may be physical, software or a combination of both. The key challenges are finding adequate Model Abstractions, Multi-formalism modelling, Model Transformation and the application of MPM techniques and tools to Complex Systems.