  Throughout the past three decades the hidden order (HO) problem in
URu$_2$Si$_2$ has remained a "hot topic" in the physics of strongly correlated
electron systems with well over 600 publications related to this subject.
Presently in 2014 there has been significant progress in combining various
experimental results embedded within electronic structure calculations using
density functional theory (DFT) to give a consistent description of the
itinerant behaviour of the HO transition and its low temperature state. Here we
review six different experiments: ARPES, quantum oscillations, neutron
scattering, RXD, optical spectroscopy and STM/STS. We then establish the
consistencies among these experiments when viewed through the Fermi-surface
nesting, folding and gapping framework as predicted by DFT. We also discuss a
group of other experiments (torque, cyclotron resonance, NMR and XRD) that are
more controversial and are presently in a "transition" state regarding their
interpretation as rotational symmetry breaking and dotriacontapole formation.
There are also a series of recent "exotic" experiments (Raman scattering, polar
Kerr effect and ultrasonics) that require verification, yet they offer new
insights into the HO symmetry breaking and order parameter. We conclude with
some constraining comments on the microscopic models that rely on localised
$5f$-U states and strong Ising anisotropy {for explaining} the HO transition,
and with an examination of different models in the light of recent experiments.
