Experimental search for neutron antineutron oscillations

The observation of neutron antineutron transitions would be direct evidence for baryon number violation. The phenomenology of the process is reviewed together with limits which can be set from existing nuclear stability experiments. The experimental requirements to carry out dedicated experiments on free neutrons is discussed and applied to an experiment now being carried out at a research reactor at the ILL, Grenoble. First results from this experiment are presented and prospects for the future reviewed