This book employs a relatively new method for solving electromagnetic problems, one which makes use of a transmission line matrix (TLM). The propagation space is imagined to be filled with this matrix. The propagating fields and physical properties are then mapped onto the matrix. Mathematically, the procedures are identical with the traditional numerical methods; however, the interpretation and physical appeal of the transmission line matrix are far superior. Any change in the matrix has an immediate physical significance. What is also very important is that the matrix becomes a launching pad for many improvements in the analysis, using more modern notions of electromagnetic waves. Eventually, the purely mathematical techniques will probably give way to the transmission line matrix method. Major revisions occur in chapters IV and VII in this second edition. The revised chapters now present an up-to-date and concise treatment on plane wave correlations and decorrelations, and provide a revised formulation of simulation to solve transient electromagnetic problems. It also takes into account semiconductors with arbitrary dielectric constant, using much smaller cell size, and extending the range of applicability and improving accuracy.