ICTS

World-sheet approach gives a procedure for computing on-shell amplitudes in string theory. However, even the tree amplitudes given by this approach suffer from divergences due to collision of vertex operators. While in some cases one can use analytic continuation to remove these divergences, this is not always possible. In contrast, string field theory provides a way to remove all such divergences and extract unambiguous, finite results for the amplitudes. We shall illustrate this with some examples.