The Giant Radio Array for Neutrino Detection (GRAND) is a proposal for a giant observatory of ultra-high energy cosmic particles (neutrinos, cosmic rays and gamma rays). It will be composed of twenty subarrays of 10 000 antennas each, to be deployed after 2030 at various locations around the world, totaling a detection area of 200 000 km². According to simulations, GRAND will reach unprecedented sensitivity to neutrinos of astrophysical origin with energies above 10^17 eV, sufficient to guarantee their detection. GRAND sub-degree angular resolution will also make it possible to hunt for point sources and possibly start neutrino astronomy. This, combined with the large instantaneous field of view expected from the location of the sub-arrays in different continents and hemispheres, will make GRAND a key instrument in the forth-coming era of multi-messenger transient astronomy, during which the century-long mystery of the nature and origin of the particles with highest energy in the Universe may be solved.