  The purpose of this review is to bridge the gap between a standard course in
quantum field theory and recent fascinating developments in the studies of
on-shell scattering amplitudes. We build up the subject from basic quantum
field theory, starting with Feynman rules for simple processes in Yukawa theory
and QED. The material covered includes spinor helicity formalism, on-shell
recursion relations, superamplitudes and their symmetries, twistors and
momentum twistors, loops and integrands, Grassmannians, polytopes, and
amplitudes in perturbative supergravity as well as 3d Chern-Simons-matter
theories. Multiple examples and exercises are included.
