Maxwell’s Treatise on Electricity and Magnetism brought about what Einstein called “the greatest change in the axiomatic basis of physics since Newton.” But Maxwell’s aim was never to construct an axiomatic theory. Instead, the Treatise presents an argument which, beginning with the most characteristic electrical and magnetic phenomena, and interpreting them as manifestations of continuous fields of electric and magnetic energy, culminates in Maxwell’s theory of light as a wave motion within those fields. The argument of the Treatise is not straightforwardly demon­strative but is a dialectical one that can be challenging to discern among the many topics presented. This book undertakes to extract and expound the principal path of Maxwell’s dialectical thinking.