  This a pedagogical introduction to scattering amplitudes in gauge theories.
It proceeds from Dirac equation and Weyl fermions to the two pivot points of
current developments: the recursion relations of Britto, Cachazo, Feng and
Witten, and the unitarity cut method pioneered by Bern, Dixon, Dunbar and
Kosower. In ten lectures, it covers the basic elements of on-shell methods.
