Magnetism is one of the most important physical phenomena. The precision measurement of magnetism gives impetus to science and technology. Various techniques, including Hall sensors, superconducting quantum interference devices, and magnetic resonance, are used for trying to improve the resolution and the sensitivity of magnetometry. In recent years, nitrogen-vacancy (NV) centers in diamond have been investigated extensively. This solid-state spin system is convenient to initialize, manipulate, and read out. It has been applied to the experimental study of quantum information and computation, and more importantly, it has displayed enormous potential applications in magnetometry. With various techniques such as dynamical decoupling and correlation spectroscopy that are being applied to NV centers, the microscopic magnetic resonance with high resolution and sensitivity has been implemented. Typical examples of these achievements are the nuclear magnetic resonance and electron paramagnetic resonance of nanoscale samples, and even of single molecules or single spins. The NV centers can also be used for precisely measuring the microwave and radiofrequency field. The issues mentioned above will be outlined in this review.