  The recent availability of precisely measured fusion cross-sections has
enabled the extraction of a representation of the distribution of barriers
encountered during fusion. These representations, obtained from a variety of
reactions, provide a direct observation of how the structure of the fusing
nuclei changes the inter-nuclear potential landscape, thus affecting the fusion
probability. Recent experiments showing the effects of static quadrupole and
hexadecapole deformation, single-- and double-phonon states, transfer of
nucleons between two nuclei, and high lying excited states are reviewed. The
application of these concepts to the explanation of the anomalous
fission-fragment anisotropies observed following reactions with actinides is
discussed.
