Spin-phonon coupling and molecular spin dynamics govern crucial processes in moleculebased imaging, optoelectronic and quantum technologies. These include contrast magnetic resonance imaging in healthcare, singlet fission for energy harvesting, ultrafast excited-state dynamics for energy transfer, long-lived optical states for optical quantum interfaces, and decoherence processes in qubits. Spin-phonon coupling also determines the performance of single-molecule magnets (SMMs), which are convenient platforms for probing fundamental molecular spin physics. SMMs are molecules that possess magnetic bistability and show magnetic memory effects at low temperature in the absence of long-range order. The timescale for magnetic memory, 𝜏, is set by the interactions of a molecule with its environment and is mediated by phonons in the solid-state, and the same interactions limit the timescale of quantum coherence when other mechanisms are suppressed. For both SMMs and molecular qubits, the goal is to slow down the spin dynamics to ensure that magnetic memory and quantum phase coherence remain for as long as possible.