  We present the calculation of dijet production, doubly-differential in dijet
mass, $m_{jj}$ and rapidity difference, $|y^{*}|$, at leading colour in all
partonic channels at next-to-next-to-leading order (NNLO) in perturbative QCD.
We consider the long-standing problems associated with scale choice for dijet
production at next-to-leading order (NLO) and investigate the impact of
including the NNLO contribution. We find that the NNLO theory provides reliable
predictions, even when using scale choices which display pathological behaviour
at NLO. We choose the dijet invariant mass as the theoretical scale on the
grounds of perturbative convergence and residual scale variation and compare
the predictions to the ATLAS 7 TeV 4.5 fb$^{-1}$ data.
