  Controlled excitation of materials can transiently induce changed or novel
properties with many fundamental and technological implications. Especially,
the concept of Floquet engineering, manipulation of the electronic structure
via dressing with external lasers, has attracted some recent interest. Here we
review the progress made in defining Floquet materials properties and give a
special focus on their signatures in experimental observables as well as
considering recent experiments realizing Floquet phases in solid state
materials. We discuss how a wide range of experiments with non-equilibrium
electronic structure can be viewed by employing Floquet theory as an analysis
tool providing a different view of excitations in solids.
