1.1 Generalized Wave Equation for an Electromagnetic Field in a Time-Varying Medium1.1.1 Generalized Derivatives1.1.2 Initial and Boundary Conditions for Electromagnetic Fields in a Time-Varying Medium1.1.3 Maxwell’s Equations in a Generalized Derivatives Representation1.1.4 Generalized Wave Equation for the Case of a Non-Dispersive Background1.1.5 Generalized Wave Equation for the Case of a Dispersive Background1.2 Fundamental Solutions to Maxwell’s Equations1.2.1 The Non-Dispersive Background1.2.2 The Dispersive Background1.2.3 A Rectangular Waveguide with Perfectly Conducting Walls1.3 Causal Time-Spatial Interpretation of Electromagnetic Field Interaction with Time-Varying Objects1.3.1 The Volterra Integral Equation for the Electromagnetic Field in a Non-Dispersive Background