Physics at MAMI C

The physics motivation for the energy increase of the Mainz Microtron from 885 to 1500 MeV (MAMI C) is presented. It is argued that the low energy regime in hadron physics where the perturbative approach to QCD is not applicable is the most relevant to further understand this peculiar theory. However, the investigation of the most significant observables needs excellent experimental precision and an intensive interaction with theory. As examples the recent measurement of the form factor of the neutron and the pion polarisability are presented. They show that the mentioned conditions are given at MAMI and will be extended by the energy increase.