  We present an overview of unbiased studies of diffuse extragalactic radio
sources. We use a previously developed filtering technique to remove compact
sources from large surveys such as WENSS, WISH, and NVSS and examine the
residual diffuse emission. A search of these residuals, unbiased by optical or
X-ray selection, has uncovered a wide variety of diffuse sources, including
those associated with groups of galaxies, ``blank'' fields, and previously
unrecognized diffuse radio galaxy emission, as well as halos and relics of rich
clusters. A second, targeted survey of the brightest X-ray clusters results in
a number of new sources, and illuminates some important selection effects. When
the well-established relationship between X-ray and radio halo luminosities is
extrapolated to lower levels, the apparent correlation holds quite well for any
type of diffuse source, even background noise. The observed correlations must
therefore be scrutinized for possible selection effects before physical
interpretations are made. We briefly mention a wide-field mapping project to
search for large-scale structures, and goals for the next generation of studies
in magnetic field - angular size parameter space.
