  Advances in scattering amplitudes have exposed previously-hidden
color-kinematics and double-copy structures in theories ranging from gauge and
gravity theories to effective field theories such as chiral perturbation theory
and the Born-Infeld model. These novel structures both simplify higher-order
calculations and pose tantalizing questions related to a unified framework
underlying relativistic quantum theories. This introductory mini-review article
invites further exploration of these topics. After a brief introduction to
color-kinematics duality and the double copy as they emerges at tree and
loop-level in gauge and gravity theories, we present two distinct examples: 1)
an introduction to the web of double-copy-constructible theories, and 2) a
discussion on the application of the double copy to calculation relevant to
gravitational-wave physics.
