Intergalactic Magnetic Field Observations and their Fundamental Implications

I will review current observational evidence for helical intergalactic magnetic fields at the ~$10^-14$ G level on ~10 Mpc length scales. The existence of magnetic fields in cosmic voids and their non-trivial helical structure suggest that they might have originated in the early universe due to CP violating fundamental interactions. The large helicity of the magnetic field suggests a possible crucial role for chiral MHD effects in the early universe.