More than 15 years ago, experiments such as SuperKamiokande and SNO showed that neutrinos can undergo 'flavour' change  and hence must have mass. Subsequent experiments, such as T2K, have precisely measured some of the key properties associated with this process, but as year no experiment has been able to measure the absolute neutrino masses.

The Enriched Xenon Observatory (EXO) project is engaged in the search for the rare 'neutrinoless double beta decay process' in which two neutrons in a nucleus simultaneously convert to protons with the emission of two electrons at a characteristic energy. Discovery of this process would provide a first measurement of the neutrino mass scale, show that neutrinos are their own anti-particle, and be the first lepton-number violating process to be observed.

EXO began searching for neutrinoless double beta decay with the EXO-200 detector in 2011. Previous results from this 200kg liquid-phase xenon time projection chamber will be presnted along with current plants for a new three-year data taking run. In parallel with these efforts,the collaboration is developing a next-generation 5-tonne scale experiment called nEXO The current status of this experiment will be presented including details of the R&D and design efforts underway.