  The inclusive jet differential cross section has been measured for jet
transverse energies, $E_T$, from 15 to 440 GeV, in the pseudorapidity region
0.1$\leq | \eta| \leq $0.7. The results are based on 19.5 pb$^{-1}$ of data
collected by the CDF collaboration at the Fermilab Tevatron collider. The data
are compared with QCD predictions for various sets of parton distribution
functions. The cross section for jets with $E_T>200$ GeV is significantly
higher than current predictions based on O($\alpha_s^3$) perturbative QCD
calculations. Various possible explanations for the high-$E_T$ excess are
discussed.
