We provide a comprehensive overview of the capabilities of optical magnetometry based on color centers embedded in a solid state environment. We review the principles of the optically detected magnetic resonance (ODMR) technique and discuss the application to the negatively charged nitrogen-vacancy (NV) center in diamond, which is our system of choice for device implementation. A comparison with other sensitive magnetometry technologies is given and it is demonstrated that NV centers in diamond allow for an unprecedented combination of spatial resolution and magnetic sensitivity in a wide range of temperatures. We show how this method can be used for measuring magnetic fields at the nanometer scale as well as for wide-field-of view magnetic field imaging. Finally, we demonstrate all-optical vector magnetometry in an ensemble of NV centers in diamond without static magnetic bias field.