  We review research on a number of situations where a quantum impurity or a
physical boundary has an interesting effect on entanglement entropy. Our focus
is mainly on impurity entanglement as it occurs in one dimensional systems with
a single impurity or a boundary, in particular quantum spin models, but
generalizations to higher dimensions are also reviewed. Recent advances in the
understanding of impurity entanglement as it occurs in the spin-boson and Kondo
impurity models are discussed along with the influence of boundaries.
Particular attention is paid to 1+1 dimensional models where analytical results
can be obtained for the case of conformally invariant boundary conditions and a
connection to topological entanglement entropy is made. New results for the
entanglement in systems with mixed boundary conditions are presented.
Analytical results for the entanglement entropy obtained from Fermi liquid
theory are also discussed as well as several different recent definitions of
the impurity contribution to the entanglement entropy.
