Emphasising the role of mathematics in describing the universe, Galileo Galilei (1564--1641) pointed out that mathematics is the language of physics (Galileo in Il Saggiatore, 1623). At the latest since the time of Isaac Newton (1643--1727), the interplay of mathematics and physics as subjects with different nature has grown increasingly important and crucial for doing physics as a science and, vice versa, theoretical physics sometimes provides suggestions for developing mathematics. In this chapter, mathematics is seen as a prerequisite for understanding physics because mathematics contributes greatly to the theoretical development of physics concepts in theoretical physics and to their empirical validation in experimental physics (see chap. 1). The development, description and processing of physics concepts by means of mathematical modelling are called physical--mathematical modelling. Physical--mathematical models are used for logical and structural integration of mathematics to describe the necessary laws and functional aspects of space--time relationships. It must nevertheless be taken into account that several empirical studies in the field of education have shown that knowledge of mathematics alone is not sufficient for good understanding and modelling of physics concepts, because mathematics has different functions in physics compared with those in mathematics it-self. This is especially so because the solutions to physics tasks do not only consist of applying mathematical methods to solving the physics tasks as mathematical tasks, but also of modelling the solution process on the basis of physics concepts. Recent research results have shown that students' learning processes---for example, their learning of physics concepts, their understanding of the epistemological development of physics, their ability to use multiple representations and their understanding of physical--mathematical modelling---appear to be correlated. Therefore, physics educators and physics teachers are recommended to take into consideration modelling-centred instruction to support and improve their students' understanding of physics concepts. In order to ensure that physics lessons and learning processes are designed and performed appropriately, it is important to address the specific features of theoretical modelling in physics and to teach physical--mathematical modelling explicitly. To describe or analyse physical--mathematical modelling, we present in this chapter several models, each of which focuses on one aspect of this complex process. Keeping the education of physics teachers in mind, we focus on the relationship between both modelling for physics teachers at university and for teaching the subject at school. In the course of this chapter, approaches to teach physical--mathematical modelling are presented and discussed on both the school and university levels (Geyer and Kuske-Janßen in Mathematics in Physics Education. Springer, Cham, pp. 75--102, 2019; Kanderakis in Sci Educ 25(7):837--868, 2016; Lehavi et al. in Mathematics in Physics Education. Springer, Cham, pp. 335--353, 2019).