Our purpose in this text is to provide an introduction to Numerical Electromagnetics, sometimes referred to as Computational Electromagnetics (CEM), a subject much too broad to cover in a single volume. Fifteen years ago, we might have found it difficult to choose between the different techniques to emphasize in our relatively brief coverage. However, due to a number of developments in the late 1980s and the 1990s, partial differential equation (PDE)-based methods, and in particular the so-called Finite Difference Time Domain (FDTD) method, have emerged as the methods with arguably the broadest range of applicability. This is especially true for electromagnetic problems involving complex and dispersive media, photonics applications, and modeling of high-speed circuits and devices. In addition, FDTD modeling of practical problems can now be undertaken with computer resources readily available to individual users. Finally, and quite importantly for our purposes, FDTD methods are relatively straightforward and intuitively follow from a physical understanding of Maxwell's equations, making this topic particularly suitable for both undergraduate and first-year graduate students in the context of a mezzanine-level course. Students with limited or no prior modeling experience will find that the FDTD method is the simplest and most insightful method from which to start their modeling education, and they can write practical and useful simulations in a matter of minutes. With an understanding of the FDTD method under their belts, students can move on to understanding more complicated methods with relative ease.