The nitrogen-vacancy (NV) defect centre in diamond is a near ideal single spin quantum probe for nanoscale magnetometry. Optically, it possesses a broad absorption band from 512-560 nm, sustained fluorescence from 630-750 nm, is chemically inert and bio-compatible, making it ideal for room-temperature applications in biology. The populations in the spin-1 sublevels of the NV ground state, which are sensitive to local magnetic fields, can be measured and polarised optically, and controlled via resonant microwave fields (~ 3 GHz). Through various quantum control schemes the NV centre has been used to detect static (DC), sinusoidal (AC) and fluctuating (FC) magnetic fields. This talk will briefly review some of the overall progress and applications of the NV centre in the detection/imaging of electronic and nuclear spins at the nanoscale, including our own work on the quantum measurement of nanodiamond-NV centres in a living cell, detection of Gd spin labels in a lipid bi-layer, and relaxtion-based electron spin resonance techniques for the non-invasive detection of magnetic species.