  In this paper we present two (a priori independent) derivations of the
eikonal operator in string-brane scattering. The first one is obtained by
summing surfaces with any number of boundaries, while in the second one the
eikonal operator is derived from the three-string vertex in a suitable
light-cone gauge. This second derivation shows that the bosonic oscillators
present in the leading eikonal operator are to be identified with the string
bosonic oscillators in a suitable light-cone gauge, while the first one shows
that it exponentiates recovering unitarity. This paper is a review of results
obtained in two previous publications of the same authors.
