  This paper presents a new event generator, ALPGEN, dedicated to the study of
multiparton hard processes in hadronic collisions. The code performs, at the
leading order in QCD and EW interactions, the calculation of the exact matrix
elements for a large set of parton-level processes of interest in the study of
the Tevatron and LHC data. The current version of the code describes the
following final states: (W -> ffbar') QQbar+ N jets (Q being a heavy quark, and
f=l,q), with N<=4; (Z/gamma* -> f fbar)+QQbar+Njets (f=l,nu), with N<=4; (W ->
ffbar') + charm + N jets (f=l,q), N<= 5; (W -> f fbar') + N jets (f=l,q) and
(Z/gamma* -> f fbar)+ N jets (f=l,nu), with N<=6; nW+mZ+lH+N jets, with
n+m+l+N<=8 and N<=3 including all 2-fermion decay modes of W and Z bosons, with
spin correlations; Q Qbar+N jets (N<=6) with t -> b f fbar' decays and relative
spin correlations included if Q=t; Q Qbar Q' Qbar'+N jets, with Q and Q' heavy
quarks (possibly equal) and N<=4; H Q Qbar+N jets (N<=4) with t -> b f fbar'
decays and relative spin correlations included if Q=t; N jets, with N<=6.
Parton-level events are generated, providing full information on their colour
and flavour structure, enabling the evolution of the partons into fully
hadronised final states.
