  Magnetic field is ubiquitous in the Universe and it plays essential roles in
various astrophysical phenomena, yet its real origin and evolution are poorly
known. This article reviews current understanding of magnetic fields in the
interstellar medium, the Milky Way Galaxy, external galaxies, active galactic
nuclei, clusters of galaxies, and the cosmic web. Particularly, the review
concentrates on the achievements that have been provided by centimeter and
meter wavelength radio observations. The article also introduces various
methods to analyze linear polarization data, including synchrotron radiation,
Faraday rotation, depolarization, and Faraday tomography.
