  I review theoretical aspects of the interaction between the accretion stream
and the disk in interacting binary systems, concentrating on recent
hydrodynamic calculations. At low accretion rates, cooling is expected to be
efficient, and the interaction leads to a nearly ballistic stream overflowing
the disk rim towards smaller radii. If cooling is ineffectual, the shocked gas
produces a bulge on the disk rim, and there is no coherent stream inward of the
disk edge. Results are presented for the mass fraction and velocity structure
of the overflowing component, and the implications for X-ray observations of
`dips', and doppler tomography of cataclysmic variables are briefly discussed.
