Neutrinoless double beta decay is a hypothetical, very slow radioactive process whose observation would establish unambiguously that massive neutrinos are Majorana particles --- that is to say, identical to their antiparticles ---, which implies that a new physics scale beyond the Standard Model must exist. Furthermore, it would prove that total lepton number is not a conserved quantity, suggesting that this new physics could also be the origin of the observed asymmetry between matter and antimatter in the Universe.In recent years, many innovative ideas have been put forward to improve the sensitivity of \bbonu\ experiments. In general, these propositions have sought to increase the number of experimental signatures available to reject backgrounds while attempting to use isotopes and detector techniques which can be more easily scaled to large masses.The objective of this project is to realize the NEXT experiment, an innovativedetector based on a high-pressure xenon gas (HPXe) TPC that will run at the Laboratorio Subterr\'aneo de Canfranc (LSC), in Spain.Our primary goal is to complete the construction and commissioning of a 150 kg HPXe TPC (NEXT-100) by 2014, and start a physics run in 2015 that can improve the present bound set by the EXO experiment and perhaps discover the Majorana nature of neutrinos. In addition, we will carry out an R\&D program focused in demonstrating the scalability of the technology to the ton scale.