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{\bf FOREWORD}

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Quantum Chromo-Dynamics (QCD), and more generally the physics of the Standard
Model (SM), enter in many ways in high energy processes at TeV Colliders, and
especially in hadron colliders (the Tevatron at Fermilab and the forthcoming
LHC at CERN), 

First of all, at hadron colliders, QCD controls the parton luminosity, which
rules the production rates of any particle or system with large invariant mass
and/or large transverse momentum.  Accurate predictions for any signal of
possible `New Physics' sought at hadron colliders, as well as the
corresponding backgrounds, require an improvement in the control of
uncertainties on the determination of PDF and of the propagation of these
uncertainties in the predictions. Furthermore, to fully exploit these new
types of PDF with uncertainties, uniform tools (computer interfaces,
standardization of the PDF evolution codes used by the various groups fitting 
PDF's) need to be proposed and developed.

The dynamics of colour also affects, both in normalization and shape, various
observables of the signals of any possible `New Physics' sought at the TeV
scale, such as, e.g. the production rate, or the distributions in transverse
momentum of the Higgs boson. Last, but not least, QCD governs many
backgrounds to the searches for this `New Physics'. Large and important QCD
corrections may come from extra hard parton emission (and the corresponding
virtual corrections), involving multi-leg and/or multi-loop amplitudes.  This
requires complex higher order calculations, and new methods have to be
designed to compute the required multi-legs and/or multi-loop corrections in a
tractable form. In the case of semi-inclusive observables, logarithmically
enhanced contributions coming from multiple soft and collinear gluon emission
require sophisticated QCD resummation techniques. Resummation is a catch-all
name for efforts to extend the predictive power of QCD by summing the large
logarithmic corrections to all orders in perturbation theory. In practice, the
resummation formalism depends on the observable at issue, through the type of
logarithm to be resummed, and the resummation methods. 

In parallel with this perturbative QCD-oriented working programme, the
implementation of both QCD/SM and New physics in Monte Carlo event generators 
is confronted with a number of issues which deserve uniformization or
improvements. The important issues are: 1) the problem of interfacing partonic
event generators to showering Monte-Carlos; 2) an implementation using this
interface to calculate backgrounds which are poorly simulated by the showering
Monte-Carlos alone; 3) a comparison of the {\tt  HERWIG} and {\tt PYTHIA}
parton shower models with the predictions of soft gluon resummation; 4)
studies of the underlying events at hadron colliders to check how well they
are modeled by the Monte-Carlo generators.

In this perspective, our Working Group devoted its activity to improvements of
the various QCD/SM ingredients relevant both for searches of `New Physics' and
estimates of the backgrounds to the latter at TeV colliders. This report
summarizes our work. Section 1 reports on the effort towards precision Parton
Distribution Functions (PDF's). Section 2 presents the issues worked out along
the two current frontiers of Higher Order QCD calculations at colliders, namely
the description of multiparton final states at Next-to-Leading Order (NLO), and
the extension of  calculations for precison observables beyond this order.
Section 3  `resummarizes\footnote{E.~Laenen \copyright, all rights reserved.}'
a large variety of questions concerning the relevance of resummation for
observables at TeV colliders. In parallel with these `general purpose tackling
angles', more specific studies, dedicated to jet physics and improved cone
algorithms, and to the QCD backgrounds to $H \to \gamma \gamma$, both
irreducible (isolated prompt photon pairs) and reducible (photon pion), are
presented in section 4. Finally, section 5 summarizes the activities of the
Intergroup on Monte Carlo issues, which are of practical interest for all three
Working Groups of the Workshop: HIGGS \cite{Cavalli:2002vs},  BSM
\cite{Azuelos:2002qw} and the present one. 

