A multiple scattering theory for the scattering of two composite parti
cles in which the clustering of the constituent particles in the proje
ctile and target is taken into account is formulated. It is shown that
the multiple scattering series can be written in terms of the transit
ion operators between the various clusters of the projectile and the t
arget. Since it is formulated in terms of transition operators between
the clusters, it can most conveniently be used in calculations such a
s cluster knock-out reactions and projectile-target fragmentation calc
ulations in heavy-ion collisions. The resulting multiple scattering se
ries reduces to the usual Watson-type multiple scattering series when
there is no clustering. A multiple scattering series for the optical p
otential is also given.