[en] Collision experiments between nuclei have in the last two decades revealed a fascinating variety of reaction phenomena, ranging from gentle elastic encounters to violent, explosion-like, fragmentations. An important class of events have been those where the identify of the reaction partners is essentially preserved during the collision process, these binary collisions from the theme of these lectures. The least violent encounters are those resulting in elastic scattering or quasielastic collisions (QEC) which comprises inelastic scattering (sometimes called quasielastic scattering (QES)) and quasielastic reactions (QER). In these reactions only a moderate amount of energy and only a few nucleons are exchanged between projectile and target. As might have been expected, the phenomena in HI reactions are not limited to QEC and fusion. A highly interesting aspect of these reactions is the presence of intermediate phenomena. This might off-hand be considered an unwanted extra complication; under appropriate conditions an outstanding new reaction phenomenon however appears, the deeply inelastic collisions (DIC). This process shares some of the characteristics of QEC such as the binary character with reaction products closely resembling the initial collision partners. In DIC however, a substantial amount of the available kinetic energy is dissipated within the collision time into internal fragment excitation, often accompanied with a somewhat larger transfer of mass. The authors concentrate on the role played by surface excitations in these two phenomena