Abstract: Rare-earth ion dopants are optically addressable solid-state spin qubits that provide numerous opportunities for studying complex quantum phenomena and developing quantum technologies. At low doping concentrations, single ions have long spin coherence, high optical indistinguishability and can connect to other nuclear spin memories in the crystal. This makes them well suited for engineering and probing entanglement both locally in their solid-state environment and at long distances by interfacing with single photons, as needed for developing quantum repeater network nodes. Towards this end, we demonstrated remote multi-partite optical entanglement between single ytterbium 171 ions coupled to nano-photonic resonators, and local quantum control of highly entangled nuclear spin memory registers. At higher doping concentrations, rare-earth ensembles can be used to mediate microwave to optical transduction, store quantum states of light, and to explore quantum many body physics like super-radiance, sub-radiance, and novel types of light-matter interference phenomena. I present our recent progress in these directions, that we explored primarily with ytterbium 171 in yttrium orthovanadate. I conclude with a discussion about future opportunities provided by this experimental platform.