  This thesis describes some of the recent (and some less recent) developments
in calculational techniques for scattering amplitudes in quantum field theory.
The focus is on on-shell recursion relations in complex momenta and on the use
of unitarity methods for loop calculations. In particular, on-shell recursion
is related to the MHV rules for computing tree-level gauge amplitudes and used
to extend the MHV rules to graviton scattering. Combinations of unitarity cut
techniques and recursion are used to argue for the "No-Triangle Hypothesis" in
N=8 supergravity which is related to its UV behaviour. Finally, combinations of
unitarity and recursion are used to demonstrate the full calculation of a
one-loop amplitude involving a Higgs particle and four gluons in the limit of
large top mass. The present version is edited to incorporate some of the
comments and suggestions of the evaluation committee, but has not been updated
for developments in the meantime.
