In the 20th Century, the Bose-Einstein Condensation (BEC) was observed in atom gases at the temperatures close to the absolute zero (Nobel Prize in Physics 2001). Then, Kavokin and co-authors have predicted and experimentally demonstrated BEC of light-matter quasiparticles, exciton-polaritons, at the room temperature. This major breakthrough in condensed matter physics paved the way to the development of polariton lasers, transistors and quantum networks.