  These lectures are centred around tree-level scattering amplitudes in pure
Yang-Mills theories, the most prominent example is given by the tree-level
gluon amplitudes of QCD. I will discuss several ways of computing these
amplitudes, illustrating in this way recent developments in perturbative
quantum field theory. Topics covered in these lectures include colour
decomposition, spinor and twistor methods, off- and on-shell recursion, MHV
amplitudes and MHV expansion, the Grassmannian and the amplituhedron, the
scattering equations and the CHY representation. At the end of these lectures
there will be an outlook on the relation between pure Yang-Mills amplitudes and
scattering amplitudes in perturbative quantum gravity.
