Neutrino-less double beta (0νββ) decay offers a unique way to probe whether neutrinos are their own anti-particles, i.e. so-called Majorana particles. It is currently searched for with detectors using 10’s to 100’s of kilograms of candidate isotopes, and tonne-scale, next generation detectors are actively being planned.

The nEXO (next-generation Enriched Xenon Observatory) is designing an ultra-low background 5-tonne, liquid xenon time projection chamber (TPC) with 0νββ half-life sensitivity of 6 x 10^27 years. nEXO is rooted in the successful EXO-200 experiment. I will present the most significant differences between EXO-200 and nEXO, describe the crucial lines of R&D we have undertaken, and illustrate our strategy to overcome the technical challenges related to this 25-fold detector scale up.