A model is a simplified representation of an aspect of the world for a specific purpose. In complex systems, many aspects are to be handled, from architectural aspects to dynamic behavior, functionalities, user-interface, and extra-functional concerns (such as security, reliability, timeliness, etc.) For software systems, the design process can then be characterized as the weaving of all these aspects into a detailed design model. Model Driven Design aims at automating this weaving process, that is automatically deriving software systems from theirs models. This paper explores the relationship between modeling and aspect weaving. It points out some of the challenges related to such automatic model weaving, illustrating them with the example of a weaving process for behavioral models represented as scenarios