[en] The CELSIUS ring at the The Svedberg Laboratory, Uppsala, is now being commissioned. The Gustaf Werner synchrocyclotron can inject into the ring, protons which are cooled, accelerated to a maximum energy of 1.36 GeV and made to interact with internal targets such as hydrogen or deuterium. Combined with a wide-angle detector for hadrons, leptons and photons, very rare meson decays can be measured and the result used for tests of the standard model. Also exotic particle searches will become possible since a very low background is anticipated around an internally circulating beam of high quality