Polarisation in CSS/GPS radio sources

The polarisation properties of the intrinsically small (< 20 kpc) radio sources are briefly discussed. At centimetric and decimetric wavelengths, substantial polarised emission is often detected in quasars and, at a lower level, in radio sources identified with galaxies with projected linear sizes in excess of a few kpc. The projected linear size at which some polarised emission is detected decreases with observing frequency. High Rotation Measures are commonly found in these sources, implying high electron/ion densities and/or strong interstellar magnetic fields. For the objects found unpolarized at resolutions of the order of a few pc, either the source magnetic field is highly disordered or the scale of ambient magnetic field cells is not resolved.