Positioning and sensing are becoming central in future wireless networks, enhancing communication, computing, and control. This chapter introduces the motivation for terrestrial solutions using cellular, Wi-Fi, Bluetooth, visible light communications (VLC), and other technologies. It further categorizes applications into public provision, enterprise, and individual services, emphasizing diverse requirements such as high accuracy, low latency, energy efficiency, and security. By outlining these motivations and challenges, the chapter establishes the foundation for the books systematic exploration of positioning and sensing over wireless networks.