This book is addressed to engineers, applied mathematicians, and physicists involved in the design and analysis of electromagnetic systems. Its chief purpose is to clarify the structure of electromagnetism. It begins with the Faraday-Maxwell insight that in electromagnetism one is faced with an interconnected dynamical system in which space and time are closely linked with physical phenomena. An appropriate basis is given via differential geometry to describe local relationships, via and topology to describe the system. These tools are introduced in the context of Maxwell's equations in the familiar vector notation. Equations are greatly simplified by the geometrical approach, and the geometrical idea of symmetry unifies the various conservation laws. This book clarifies the relationship between fields, potentials, and sources. Links between macroscopic and quantum phenomena are explored from a geometric angle and there is a simple discussion of superconductivity.