This accessible text, now in its second edition, explains the key principles of transmission lines using straightforward mathematics, extensive illustrations and practical worked examples. The early chapters use a lossless equivalent circuit to derive the basic theory, demonstrating how pulses and sine waves perform in simple transmission line circuits. Later chapters develop this model by demonstrating the derivation of circuit parameters, and the use of Maxwell's equations to extend this theory to major transmission lines. The second edition has been revised and expanded to emphasise the role of electromagnetic waves and photons in all transmission lines, providing valuable insight into the fundamental physics. New topics include sine waves in the time domain, multiple junctions, and attenuation in the presence of standing waves. Covering DC to optical frequencies, this book is an invaluable resource for students, researchers and professionals in electrical, microwave and optical engineering as well as applied physics.