We present a summary of the Hadronic Final States parallel sessions of the DIS99 workshop. Topics were presented over two days and included both theoretical and experimental talks. Recent progress in the understanding of QCD in deep inelastic scattering, e + e − collisions, and in γ and p collisions was discussed.
THEORY SUMMARYDuring the parallel sessions of the Hadronic Final States Working Group about forty talks were presented. Out of these, about ten might be classified as theoretical ones. The issues they discussed ranged from instantons to heavy flavour production to higher order QCD calculations. It is therefore understandable how difficult it might be to try to provide an organic summary of such a widespread collection of interesting topics.We shall therefore try to highlight here what we consider to be the main points of the various contributions, leaving the task of properly introducing and explaining the subject to the individual summaries. Such summaries will not be cited explicitly in this section, since they can easily be found in these proceedings under the name of the person who gave the presentation.A common feature can be identified in almost all the talks given. They clearly focus on the need to go beyond standard fixed next-to-leading order (NLO) QCD perturbation theory as the quality of the experimental data demands more accurate theoretical calculations.G. Salam and H. Jung both described phenomenological studies related to the CCFM equation. This is an evolution equation that goes beyond the so-called "multi-Regge" limit of the BFKL equation, and also tries to implement effects due to colour coherence (via angular ordering) and soft particles. As CCFM is harder to solve than BFKL, the question is how similar the predictions of the two approaches are. Salam argued that, with the inclusion of soft effects, BFKL and CCFM can be shown to lead to identical predictions at the leading log level. Differences at sub-leading level, as well as ambiguities in the implementation of the equations at this level, do however remain. Jung described a practical implementation of the CCFM equation in the program SMALLX and showed that a good phenomenological description of both F 2 and forward jets data can be achieved.Small-x logarithms are not the only ones appearing in a QCD perturbative expansion. N. Kidonakis described how to take care of the large logs resulting from soft gluon emissions when final states are produced near threshold. Resummed expressions for these terms have been written some time ago, but until recently it was still unclear how to treat these expressions so that the final result would indeed only contain the resum-