  The work on black holes immersed in external fields is reviewed in both
test-field approximation and within exact solutions. In particular we pay
attention to the effect of the expulsion of the flux of external fields across
charged and rotating black holes which are approaching extremal states.
Recently this effect has been shown to occur for black hole solutions in string
theory. We also discuss black holes surrounded by rings and disks and rotating
black holes accelerated by strings.
