Magnetic fields at galactic and larger scales is a challenging issue for astrophysics and cosmology. In this talk, I'll review the methods to detect magnetic fields at these scales as well as I'll revise the field structure of the Milky Way and its dynamical implications over the gas distribution. In the second part, I'll review the updated works about effects of primordial magnetic fields on large scale structure and I'll show you preliminary results on its imprint on cosmic microwave background.