  This report was prepared in the context of the LPCC "Electroweak Precision
Measurements at the LHC WG" and summarizes the activity of a subgroup dedicated
to the systematic comparison of public Monte Carlo codes, which describe the
Drell-Yan processes at hadron colliders, in particular at the CERN Large Hadron
Collider (LHC). This work represents an important step towards the definition
of an accurate simulation framework necessary for very high-precision
measurements of electroweak (EW) observables such as the $W$ boson mass and the
weak mixing angle. All the codes considered in this report share at least
next-to-leading-order (NLO) accuracy in the prediction of the total cross
sections in an expansion either in the strong or in the EW coupling constant.
The NLO fixed-order predictions have been scrutinized at the technical level,
using exactly the same inputs, setup and perturbative accuracy, in order to
quantify the level of agreement of different implementations of the same
calculation. A dedicated comparison, again at the technical level, of three
codes that reach next-to-next-to-leading-order (NNLO) accuracy in quantum
chromodynamics (QCD) for the total cross section has also been performed. These
fixed-order results are a well-defined reference that allows a classification
of the impact of higher-order sets of radiative corrections. Several examples
of higher-order effects due to the strong or the EW interaction are discussed
in this common framework. Also the combination of QCD and EW corrections is
discussed, together with the ambiguities that affect the final result, due to
the choice of a specific combination recipe.
