Multi-Paradigm Modeling (MPM) addresses the necessity of using multiple modeling paradigms when designing complex systems. Because of its multi-disciplinary nature, the MPM field involves research teams with technical backgrounds as different as control science, model checking, modeling language engineering or system-on-chip development. In this paper, we propose to explore the MPM domain through a survey of existing techniques from different horizons. Since the heterogeneity of models is at the heart of Multi-Paradigm Modeling, we first identify the sources of this heterogeneity and introduce the problems it raises. Then we show how the different existing techniques address these problems.