  During the final phases of inspiral, a massive black hole (MBH) binary
experiences a recoil due to the asymmetric emission of gravitational waves. We
use recent results from numerical relativity simulations together with models
of the assembly and growth of MBHs in hierarchical cosmologies, to study the
dynamics, statistics, and observability of recoling MBHs. We find that, at
redshift z<3, kicked non-rotating holes are typically found between 1 and 30
kpc from their galaxy centers, while rapidly rotating ones are typically
between 10 and a few hundred kpc. A recoiling hole that carries an accretion
disk may shine as an "off-nuclear AGN" while it moves away from the center of
its host galaxy. We predict that, depending on the hole spin distribution and
the duration of their active phase, a population of off-nuclear AGN may already
be detectable at low and intermediate redshifts in present deep Hubble Space
Telescope observations. The James Webb Space Telescope may discover tens of
wandering AGN per square degree, most of them moving within their host halos on
unbound trajectories.
