This book has two purposes. The first is to examine the electromagnetic theory behind many of the calculations relevant to the design of high voltage overhead transmission lines. These include electromagnetic propagation on multiple parallel wires above the earth and their associated fields, electrostatic fields near more complicated geometries, limitations on power transfer capability, corona onset and its effects, electromagnetic compatibility with other systems that share the transmission line right of way and grounding systems. The second is to show how the more general theory reduces to the theory commonly used by practicing engineers. This includes understanding both the physical and mathematical approximations made for simplified analysis. In describing these, some practical aspects of designing high voltage transmission lines are discussed. Included are discussions of why common transmission line topologies are used, the relation between electric fields and many design parameters, ampacity and sag calculations, and techniques for increasing power transfer capability. In the second edition of the book additional material has been added to help the reader understand why overhead lines are used, why they are designed the way they are and how they interact with systems that share the right of way.