The nitrogen vacancy (NV) center in diamond is an atomic-scale defect that exhibits remarkably coherent quantum properties in a uniquely accessible way: at room temperature, in ambient conditions, and even immersed in biological environments. NV centers are being explored for a variety of quantum technologies, including quantum sensing and quantum information processing. In this talk, I introduce the physics and materials science behind the success of the NV center and I highlight some of the major achievements of NV-based quantum sensors, the most advanced of NV-based technologies. I present a versatile NV-based imaging platform where we have incorporated an NV center into a scanning probe microscope and used it to image vortices in superconductors , skyrmions in thin film magnetic multilayers, and conductivity on the nanoscale. I also outline the challenges facing the widespread use of NV centers in quantum applications. One major challenge is mitigating surface-induced quantum decoherence, a universal problem that affects many quantum technologies. With its sensitivity to electric and magnetic fields over a wide range of frequencies, we have used the NV center as a noise spectrometer [2,3] to spectroscopically probe sources of surface and bulk-related decoherence, differentiating between electric and magnetic origins. These studies guide the ongoing development of quantum control and diamond surface preparation techniques, pushing towards the ultimate goal of NV-based single nuclear spin imaging.
 M. Pelliccione et al, Nature Nanotechnology 11, 700 (2016)
 B. Myers et al, PRL 113, 027602 (2014)
 B. Myers et al, PRL 118, 197201 (2017)