We still do not have a fully satisfactory theory of the origin of cosmic magnetic fields. Placing constraints of these fields could play an important role in deciding which of the models are likely to be the plausible ones. The polarization and power spectrum of CMBR could be an important probe in this endeavor. The focus of the talk will be to show how the polarization, power spectrum, bispectrum and trispectrum could place constraints on the strength of these fields.