Magneto-optical (Faraday) rotation is a process in which the plane of light polarization rotates as light propagates through a medium along the direction of a magnetic field. In atomic vapors where ground state atomic polarization relaxes very slowly (relaxation rates ≳1 Hz), there arise ultranarrow, light-power-dependent (nonlinear) features in the magnetic field dependence of Faraday rotation. The shot-noise-limited sensitivity of a magnetometer based on nonlinear Faraday rotation can exceed10−11 G/Hz,corresponding to a sensitivity of∼10−6 Hz/Hzto Zeeman sublevel shifts. Here we discuss recent progress in magnetometry based on nonlinear optical rotation and consider the application of these methods to searches for fundamental-symmetry-violating interactions. ©2001 American Institute of Physics.