  Grazing incidence x-ray surface scattering has been used to investigate
liquid surfaces down to the molecular scale. The free surface of water is well
described by the capillary wave model (<z(q)z(-q)> ~ q-2 spectrum) up to
wavevectors > 10^8 m^-1. At larger wavevectors near-surface acoustic waves must
be taken into account. When the interface is bounded by a surfactant monolayer,
it exhibits a bending stiffness and the bending rigidity modulus can be
measured. However, bending effects generally cannot be described using the
Helfrich Hamiltonian and the characteristic exponent in the roughness power
spectrum can smaller than 4. Finally, upon compression, tethered monolayers
formed on a subphase containing divalent ions are shown to buckle in the third
dimension with a characteristic wavelength on the order of 10^8 m^-1.
