  This review describes the duality between color and kinematics and its
applications, with the aim of gaining a deeper understanding of the
perturbative structure of gauge and gravity theories. We emphasize, in
particular, applications to loop-level calculations, the broad web of theories
linked by the duality and the associated double-copy structure, and the issue
of extending the duality and double copy beyond scattering amplitudes. The
review is aimed at doctoral students and junior researchers both inside and
outside the field of amplitudes and is accompanied by various exercises.
