  This is a short review of recent x-ray diffraction studies of the phases and
phase transitions of thermotropic liquid crystals. The areas covered are
twist-grain-boundary phases, antiferroelectric phases studied with resonant
x-ray diffraction, and smectic phases within gel structures. In all areas x-ray
diffraction has played a key role. Nonetheless open questions remain: the
nature of the smectic-C variant of the twist-grain-boundary phase, the origin
of antiferroelectric phases, and whether novel Bragg glass states exist for
smectic-A gel samples.
