Nitrogen-vacancy (NV) centers in diamond are atomic-scale spin systems with remarkable quantum properties that persist to room temperature. They are highly sensitive to a wide variety of fields (magnetic, electric, thermal) and are easy to initialize, read-out, and manipulate on the individual spin level; thus they make excellent nanoscale sensors. The NV’s sensitivity is a double-edged sword however; environmental fluctuating fields are also a source of decoherence. We use the NV to probe these fluctuating fields, both their frequency spectrum and spatial character, and we mitigate their induced decoherence through engineered CVD diamond growth and quantum control of the NV. I will also present my group’s work on quantum assisted sensing of strain fields on the nanoscale. We demonstrate strain coupling of a single NV spin to a high quality factor mechanical mode of a single-crystal diamond mechanical resonator. This hybrid system has exciting prospects for a phonon-based approach to integrating NVs into quantum networks.