  The first measurements of the diffractive structure function $F_2^{D(3)}$ at
HERA are discussed. A factorisable interpretation in which a partonic structure
is assigned to the pomeron is investigated through QCD analyses in which both
the quark and gluon densities are permitted to vary freely. A method of
measuring the longitudinal structure function of the pomeron without changing
the $ep$ centre of mass energy is presented. The possibility that the pomeron
structure may receive a large contribution from gluons, relative to quarks, at
high $\beta$ is highlighted, and the experimental signatures which may support
such a structure are reviewed.
