Non-terrestrial networks (NTN) are comprised of satellites — geostationary equatorial orbit (GEO), medium-Earth orbit (MEO) and low-Earth orbit (LEO) — as well as high-altitude platform systems (HAPS), which include unmanned airships or airplanes above 20 km, and unmanned aerial systems (UAS) or drones. In this white paper, we describe the challenges and the solutions of the NTN system and the importance of standards-based NTN solutions (Release 17 through future Releases 18 and 19), especially for LEO-based 5G NR and 4G NB-IoT/eMTC.