Perturbative QCD and Regge theory: closing the circle

We explain how Regge theory and perturbative evolution may be made compatible at small x. The result not only gives striking support to the two-pomeron description of small-x behaviour, but gives a rather clean test of perturbative QCD itself. When x is very small, the protonʹs gluon distribution function is significantly larger than is commonly believed. Perturbative evolution is invalid below Q2≈5 GeV2.