  We derive a perturbative expansion for space time entanglement entropy in
string theory by comparing replica trick constructions on the target space and
on the worldsheet. Requiring the two approaches to match implies a set of
constrains on the amplitudes involved and produces a non-trivial relation among
target space and world sheet entanglement. We will be mainly interested in
bosonic string on a flat background but also discuss the superstring
generalization.
