  The latest results from the H1 and ZEUS collaborations which challenge the
QCD description of high energy $ep$ collisions are presented. Data from HERA
continue to provide precision measurements and are compared to the latest
theoretical predictions. Measurements of new processes are also presented as
well as investigation of regions where perturbative QCD fails to describe the
data. Four themes are presented here. Measurements of hard QCD processes,
prompt photon and jet production, are used to compare to the latest theoretical
predictions and, in the case of jet production, used to make high-precision
extractions of the strong coupling constant up to next-next-to-leading order in
QCD. All H1 and ZEUS charm and beauty cross sections in deep inelastic
scattering have been combined and used to extract heavy-quark masses, including
the running of the charm-quark mass with the scale of the process.
Factorisation in diffraction has been investigated in charm production in deep
inelastic scattering and prompt photon production in diffractive
photoproduction has been measured for the first time. Finally, the inclusive
data on deep inelastic scattering is presented in various forms in order to
allow investigation of the underlying mechanism at very low photon virtuality
$Q^2$ and low Bjorken $x$.
