The multi-messenger astronomy aims to study astrophysical events through different messengers : GW, photons, neutrinos. The 170817 joint detection of GW and photons (at all wavelengths) has proven the relevance of multi-messengers studies. Yet it also showed the necessity of coordination and preparation of electromagnetic observations (from gamma to radio) to have relevant constraints on physical parameters. In this talk, I will present the Global Rapid Advanced Network Devoted to the Multi-messenger Addicts (GRANDMA), a network of telescopes aiming to detect, identify and characterize electromagnetic counterparts to gravitational-wave sources. I will detail the consortium, its capabilities, scientific program and public tools developed for the time domain astronomy. I will conclude by presenting a summary of our scientific results after O3 LIGO/Virgo run and the prospects we will be conducting to prepare the next GW observation runs (and possibly KM3NET campaigns).