Telecommunications have been evolved from a store-and-forward to a compute-and-forward paradigm. Such change (making computing the core of communications) has been possible, thanks to network virtualization and softwarization. However, legacy and future communication networks based on classical physics present some intrinsic limitations that will be impossible to exceed. Such horizons are going to mainly bound performance of security, latency, and communication efficiency. The only way to go beyond these edges is an intrinsic change of paradigm, where telecommunications exploit quantum mechanics. By employing quantum-mechanical characteristics of nature, future communication networks can achieve unexpected performances in an efficient way. The clarification of such context and the reasons behind the deployment of quantum mechanics in telecommunications are the central theme of this introductory chapter.