  In this thesis we consider the phenomenology of QCD, with particular
reference to the ongoing experimental program at the Large Hadron Collider in
CERN. The current progress in precision measurement of Standard Model processes
at the LHC experiments must be matched with corresponding precision in
theoretical predictions. Such calculations are vital if we are to untangle
signals of New Physics from LHC data. We consider in particular the amplitudes
for five parton interactions at 1- and 2-loop order and present analytic
results in terms of rational functions multiplying a basis of master integrals.
We address the problem of the solution of a system of integration-by-parts
identities for Feynman integrals and demonstrate how some current difficulties
may be mitigated. We consider also the properties of the top quark, and present
the real-virtual contributions to the calculation of its decay rate. These
amplitudes constitute a necessary ingredient in the complete calculation of top
quark pair production and decay at NNLO. Turning to phenomenology, we consider
the extraction of two important SM parameters, the top mass and the strong
coupling constant, from measurements of top pair production at the ATLAS and
CMS experiments. We compare with NNLO theory predictions and extract the
parameters simultaneously. We find values which are compatible with the current
world averages published by the PDG. Finally, we examine the circumstances in
which a heavy quark can be considered a constituent of the proton. We look at
the production of a Higgs boson in association with b quarks in schemes in
which the b may or may not be included in the initial state. We show that
predictions in both schemes are well-motivated, and moreover that both are
consistent provided a judicious choice of scales is made. We suggest a typical
scale choice somewhat lower than the typical hard scale of the process.
