Defects in solids are in many ways analogous to trapped atoms or molecules. They can serve as long-lived quantum memories and efficient light-matter interfaces. As such, they are leading building blocks for long-distance quantum networks and distributed quantum computers. This paper describes the quantum-mechanical coupling between atom-like spin states and light, using the diamond nitrogen-vacancy (NV) center as a paradigm. We present an overview of the NV center’s electronic structure, derive a general picture of coherent light-matter interactions, and describe several methods that can be used to achieve all-optical initialization, quantum-coherent control, and readout of solid-state spins. These techniques can be readily generalized to other defect systems, and they serve as the basis for advanced protocols at the heart of many emerging quantum technologies.