Hadronization

Hadronization corrections to the predictions of perturbative QCD are reviewed. The existing models for the conversion of quarks and gluons into hadrons are summarized. The most successful models give a good description of the data on $e^+e^-$ event shapes and jet fragmentation functions, and suggest that the dominant hadronization effects have a $1/Q$ dependence on the hard process energy scale $Q$. In several cases the $1/Q$ terms can be understood in terms of a simple longitudinal phase-space model. They can also be inferred by relating non-perturbative renormalon effects to the infrared cutoff dependence of perturbative contributions.