  The study of the top quark has a central role for both the ATLAS and CMS
experiments. The measurement of the $t\bar{t}$ production differential cross
section, in particular, is sensitive to existence of new resonances, it is a
stringent test of perturbative QCD calculations and it is used to improve the
modelling of $t\bar{t}$ production. ATLAS and CMS provided a large number of
results during the last years at $\sqrt{s}$=7, 8, 13 TeV, in different regions
of the phase space, considering different channels and topology and measuring
the cross section as a function of the kinematic variables of the $t\bar{t}$
system, the top quarks and/or their decay products. Even if the individual
steps are dependent on the specific analysis all the differential cross section
measurements proceed through the same workflow: the event selection, the
background determination, the reconstruction of the $t\bar{t}$ system, the
definition of the fiducial phase space, the unfolding applied to remove the
effect of limited acceptance and resolution of the detector and the evaluation
of the systematic uncertainties. In the following I will focus on the
techniques used by ATLAS and CMS to perform some of these steps while
presenting a selection of recent results by the two experiments.
