Quantum sensing techniques using nitrogen-vacancy (NV) spin probes in diamond present a promising approach to performing magnetic resonance imaging and spectroscopy at the nanoscale under ambient conditions. In this talk I will focus on new techniques based on controlled cross-relaxation between the quantum probe and target system. Experimental demonstrations of both electron and nuclear spin resonance using these techniques will be described, including applications in chemical detection, bio-magnetic characterisation, and hyperpolarisation of nuclear spins external to the diamond substrate.