A description is given of the radioactive ion beam facility, SIRIUS, proposed to be built at ISIS, the world leading pulsed neutron source. Up to 100 &mgr;A of 800 MeV protons from the ISIS synchrotron will be taken down a new beam line into a target station complex where radioactive nuclei will be formed as a result of the interaction with the target. The nuclei are subsequently ionised and accelerated to 200 kV. The beam passes through a broad range spectrometer to provide several beams of different ion species simultaneously. One beam passes through a high resolution spectrometer and is accelerated in an RFQ and a superconducting linear accelerator to 10 MeV/amu, for nuclear physics research. The other beams are taken to a low energy experimental area. ©1999 American Institute of Physics.