  The dynamics of charged particles in electromagnetic fields is an essential
component of understanding the most extreme environments in our Universe. In
electromagnetic fields of sufficient magnitude, radiation emission dominates
the particle motion and effects of nonlinear quantum electrodynamics (QED) are
crucial, which triggers electron-positron pair cascades and counterintuitive
particle-trapping phenomena. As a result of recent progress in laser
technology, high-power lasers provide a platform to create and probe such
fields in the laboratory. With new large-scale laser facilities on the horizon
and the prospect of investigating these hitherto unexplored regimes, we review
the basic physical processes of radiation reaction and QED in strong fields,
how they are treated theoretically and in simulation, the new collective
dynamics they unlock, recent experimental progress and plans, as well as
possible applications for high-flux particle and radiation sources.
