Radin Dardashti (MCMP/LMU) gives a talk at the MCMP Colloquium (2 July, 2014) titled "On the Distinction between Internal and External Symmetries". Abstract: There is no doubt that symmetries play an important role in fundamental physics, but there is no agreement among physicists on what this role exactly is. So it is not surprising that it has caught the interest of philosophers in recent years leading to a lively discussion on the epistemological and ontological significance of symmetries. Especially in this context it becomes relevant whether common distinctions made between different kinds of symmetries are purely conventional or have a deeper mathematical and/or physical justification. It is the aim of this talk to discuss the distinction between internal and external (or spacetime) symmetries and its possible justification. First, I will discuss attempts at combining internal and external symmetries, which lead to several no-go theorems. A naive interpretation of these results leads to the conclusion that the distinction is physically/mathematically justified. Second, the strong dependence of the no-go results on physical and mathematical assumptions is discussed and it is shown how the distinction becomes blurred once mathematical assumptions are weakened. This is exactly what happens in supersymmetric extensions of the standard model of particle physics. So, in the final part, I will argue that under a certain (philosophical) assumption the question about the status of the distinction can be made into an experimental question.