Electronic and nuclear spins associated with defects in solids comprise a promising platform for the realization of practical quantum technologies. A prominent example is the nitrogen‐vacancy center in diamond, for which many techniques for coherent manipulations and local entanglement operations are already available and employed, for example, for nanoscale sensing applications. However, despite this impressive progress in the control of individual spin qubits in diamond and other materials, the problem of coherently integrating many spin qubits into larger networks is still unsolved. In light of the ongoing progress in the fabrication of diamond beams and waveguides of increasing optical and mechanical quality, we introduce and analyze in this project a new approach for a scalable quantum‐technology platform: Phonon quantum networks, where quantum states encoded in long‐lived spin states of silicon‐vacancy (SiV) centers in diamond are coupled via propagating phonons in waveguides and coupled resonator arrays. The main objective of this project is to provide a detailed theoretical analysis of such acoustic cavity QED and waveguide QED systems and to identify optimized control schemes for the implementation of coherent defect‐phonon interactions, phonon‐mediated entanglement operations and state‐transfer protocols between distant spin qubits. In addition, we will explore new physical effects and applications beyond quantum information processing, which arise from strong coherent and dissipative interactions between spin‐, phononic‐ and photonic degrees of freedom. This includes studies related to the formation and propagation of new hybridized quasi‐particles, phonon superradiance and phonon amplification, as well as more general investigations of energy transport phenomena in microscopic (quantum) networks. By addressing both conceptually new as well as practically relevant aspects, this project will provide an important theoretical basis for upcoming experimental realizations of phonon networks.