  These lectures are a brief introduction to scattering amplitudes. We begin
with a review of basic kinematical concepts like the spinor helicity formalism,
followed by a tutorial on bootstrapping tree-level scattering amplitudes.
Afterwards, we discuss on-shell recursion relations and soft theorems,
emphasizing their broad applicability to gravity, gauge theory, and effective
field theories. Lastly, we report on some of the new field theoretic structures
which have emerged from the on-shell picture, focusing primarily on
color-kinematics duality.
