  Following the detection of polarized diffuse Galactic emission in 1962 a
number of surveys were undertaken at low frequencies in the following years
resulting in important insights on the local magnetic field, polarization of
the giant radio loops and other Galactic structures, as well as on the
properties of the diffuse magnetized interstellar medium. This field of
research experienced a revival in the eighties and nineties by a number of high
resolution observations at low and high frequencies, which showed a large
variety of polarization structures having no corresponding signature in the
total intensity images. 'Canals' and 'Faraday screens' were reported, which
clearly indicate that Faraday rotation in the magneto-ionic medium may largely
vary on small scales. These findings called for a systematic approach and a
number of new unbiased polarization surveys were started. Also new attempts for
absolute calibration are under way, which is a critical issue when interpreting
polarization structures. This paper reviews polarization survey projects and
also summarizes recent results and interpretations of this rather active field
of research.
