  This is an extended version of our short report hep-th/0603001, where a
holographic interpretation of entanglement entropy in conformal field theories
is proposed from AdS/CFT correspondence. In addition to a concise review of
relevant recent progresses of entanglement entropy and details omitted in the
earlier letter, this paper includes the following several new results : We give
a more direct derivation of our claim which relates the entanglement entropy
with the minimal area surfaces in the AdS_3/CFT_2 case as well as some further
discussions on higher dimensional cases. Also the relation between the
entanglement entropy and central charges in 4D conformal field theories is
examined. We check that the logarithmic part of the 4D entanglement entropy
computed in the CFT side agrees with the AdS_5 result at least under a specific
condition. Finally we estimate the entanglement entropy of massive theories in
generic dimensions by making use of our proposal.
