Secure communication is a cornerstone of modern society, underpinning everything from financial transactions to critical infrastructure. As classical encryption faces growing threats from advancing computational power, quantum communication offers a fundamentally secure alternative, leveraging the laws of physics to protect data. We introduce QuaNTUM (Quantum Network at the Technical University of Munich), a modular and extensible quantum communication testbed designed to enable scalable, flexible, and secure quantum communication across fiber-based campus networks and satellite-ground links. QuaNTUM integrates early deployments of solid-state quantum emitters in small satellites, bridging terrestrial and free-space channels. As an open-access platform, it supports experimental quantum communication protocols, quantum device benchmarking, and hybrid network integration. The terrestrial network connects universities and research institutes across the high-tech campus in Garching near Munich, using single-mode fibers in a star-shaped topology. Each node features polarization-maintaining components, multiplexers, and time-synchronized analysis modules, with a central switching hub for dynamic routing. Active polarization control and real-time feedback ensure low error rates and stable qubit transmission, enabling high-fidelity quantum key distribution (QKD) and entanglement distribution. A central focus of QuaNTUM is its use of deterministic single-photon sources based on optically active defects, such as in hexagonal boron nitride (hBN) or excited erbium atoms. These sources are currently being deployed in orbit, marking one of the first demonstrations of a solid-state quantum emitter in space. By uniting fiber and free-space links with scalable hardware and open protocols, QuaNTUM offers a basis that could adapt to future hybrid quantum networks, supporting both current testbed research and the long-term vision of a global quantum internet.