In this paper we present two (a priori independent) derivations of the
eikonal operator in string-brane scattering. The rst 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 identied with the string bosonic oscillators in a suitable light-cone gauge,
while the rst one shows that it exponentiates recovering unitarity. This paper is a
review of results obtained in Refs. [1]. and [2].