  Observations of magnetic fields on scales up to several Mpc are important for
understanding cluster and large-scale structure evolution. Our current census
of such structures is heavily biased -- towards fields of several microG,
towards fields in deep potential wells, and towards high inferred field
strengths in cooling flow and other clusters from improper analysis of rotation
measure data. After reviewing these biases, I show some recent results on two
relics that are powered in very different ways. I describe new investigations
that are now uncovering weak diffuse fields in the outskirts of clusters and
other low density environments, and the good prospects for further progress.
