QCD Radiation in Top-Antitop and Z+jets Final States : Springer : 9783319196527 : 3319196529 : 25 Jun 2015 : This thesis contains new research in both experimental and theoretical particle physics, making important contributions in each. Two analyses of collision data from the ATLAS experiment at the LHC are presented, as well as two phenomenological studies of heavy coloured resonances that could be produced at the LHC. The first data analysis was the measurement of top quark-antiquark production with a veto on additional jet activity. As the first detector-corrected measurement of jet activity in top-antitop events it played an important role in constraining the theoretical modelling, and ultimately reduced these uncertainties for ATLAS's other top-quark measurements by a factor of two. The second data analysis was the measurement of Z+2jet production and the observation of the electroweak vector boson fusion (VBF) component. As the first observation of VBF at a hadron collider, this