The fusion of terrestrial and non-terrestrial networks promises to bridge the connectivity gap for remote places and improve connectivity for those already online. This amalgamation heralds a significant shift in both technological impact and social progress, charting a course for long-term advancements. It marks a substantial collaborative challenge for the mobile and satellite communications sectors to design and manage a novel three-dimensional wireless network architecture. In its Release 17, the Third-generation partnership project (3GPP) has taken an important step towards this integration by standardizing non-terrestrial networks (NTN), enabling 5G terrestrial infrastructures supporting NTN framework. This framework is intended to include a network of low Earth orbit (LEO) satellites, with the inclusion of unmanned aerial vehicles (UAVs) and hhigh altitude platforms (HAPs) serving as distinct NTN use cases. However, like the global positioning system (GPS), NTN signals struggle to penetrate indoor environments due to attenuation and scattering by physical barriers such as roofs and walls. Furthermore, the constraints of power and latency present considerable challenges to ensuring reliable,seamless coverage and low-latency communication for cellular devices utilizing NTN. This chapter provides an overview of NTNs and their integration into terrestrial networks (TN). We also provide information on various use cases of NTN and how the NTN can be integrated with 5G communication systems.