  The GRAND project aims to detect ultra-high-energy neutrinos, cosmic rays and
gamma rays, with an array of $200,000$ radio antennas over $200,000\,{\rm
km}^2$, split into $\sim 20$ sub-arrays of $\sim 10,000\,{\rm km}^2$ deployed
worldwide. The strategy of GRAND is to detect air showers above $10^{17}\,$eV
that are induced by the interaction of ultra-high-energy particles in the
atmosphere or in the Earth crust, through its associated coherent
radio-emission in the $50-200\,$MHz range. In its final configuration, GRAND
plans to reach a neutrino-sensitivity of $\sim 10^{-10}\,{\rm GeV}\,{\rm
cm}^{-2}\,{\rm s}^{-1}\,{\rm sr}^{-1}$ above $5\times 10^{17}\,$eV combined
with a sub-degree angular resolution. GRANDProto300, the 300-antenna pathfinder
array, is planned to start data-taking in 2021. It aims at demonstrating
autonomous radio detection of inclined air-showers, and study cosmic rays
around the transition between Galactic and extra-Galactic sources. We present
preliminary designs and simulation results, plans for the ongoing, staged
approach to construction, and the rich research program made possible by the
proposed sensitivity and angular resolution.
