The top quark is the most massive fundamental particle of the Standard Model of particle physics, and as the only quark to decay before hadronising gives a unique opportunity for studying QCD, the theory of the strong interaction. In this thesis, we study the tt production cross-section as a function of several variables related to the produced top quarks. This thesis presents variables defined after the hadronisation of the top quark, and so are mostly independent of its theoretical description, unlike previous results which are corrected to the partonic variables. Using the ATLAS detector at the LHC, the measurements are performed for √s = 7 TeV proton–proton collisions. The measurements are sensitive to various parameters entering the description of top quark production, including the Parton Distribution Functions, and so have good potential to be used in furthering our understanding of proton collision physics and for future tunings of the models used in describing the physics.