In a bottom-up approach anomaly-free R symmetries as extensions of the MSSM are classified and analyzed for their phenomenological properties. In the second part of the talk, these R symmetries are disproven to originate from 4d SUSY GUTs because otherwise they would predict massless exotics. However, in the final part it is shown that these R symmetries can indeed originate from higher dimensions, i.e. from the compactification of the heterotic string on orbifolds.
