This thesis considers aspects of nonlinear electromagnetism and the eects of spin under the in uence of extreme elds. Born-Infeld-like theories are studied in the context of possible slow light experiments. Maximum amplitude plasma waves are considered as a possible testing ground for nonlinear electrodynamics with regards to electron energy gain. Finally the eects of the coupling between the electromagnetic eld and the spin of a relativistic classical particle are considered via a new derivation of the relativistic Stern-Gerlach and Thomas- Bargmann-Michel-Telegdi equations. These equations are then paired with the Nakano-Tulczyjew condition and, as the Stern-Gerlach-type terms in the equations of motion are most prominent in a eld with a high eld gradient, the impact of spin is investigated in the context of a maximum amplitude plasma wave.