  Modes have steadily influenced the understanding of physical systems through
time. At least since the prediction of the Casimir effect, they also play a
very important role in Casimir Physics and in the understanding of the
different phenomena typical of this research field. At equilibrium modes
provide a direct connection between the zero-point energy and the existence of
irreducible fluctuations in a quantum system, offering an anatomic view into
the physics of the interaction. In nonequilibrium systems, modes can be
decisive to understand the behavior of quantum fluctuation-induced phenomena,
highlighting key aspects which determine their strength and their functional
dependence. In this article we review some recent studies and results that
highlight how modes impact Casimir physics and the central role they play in
shaping our understanding of this area of research.
