  This survey is focused on two asymptotic models for internal waves, the
Benjamin-Ono (BO) and Intermediate Long Wave (ILW) equations that are
integrable by inverse scattering techniques (IST). After recalling briefly
their derivations we will review old and recent results on the Cauchy problem,
comparing those obtains by IST and PDE techniques and also results more
connected to the physical origin of the equations. We will consider mainly the
Cauchy problem on the real line with only a few comments on the perodic case.
We will also briefly discuss some relevant problems, in particular the higher
order extensions and the two-dimensional (KP like) versions of the BO and ILW
equations.
