“It is our responsibility as scientists, knowing the great progress which comes from a satisfactory philosophy of ignorance, the great progress which is the fruit of freedom of thought, to proclaim the value of this freedom, to teach how doubt is not to be feared but welcomed and discussed; and to demand this freedom as our duty to all coming generations� —— Richard Feynman, 1955 —— First, as students from Cal Tech and MIT and then as researchers and teachers from other universities and industry, we are bene?ted greatly from the philo- phy of learning practiced by these and other distinguished universities in the US, namely, learn and teach the fundamentals and not the fashions. Under this guiding light, this comprehensive book was formed, covering the most important modern topics on guided waves. As such, it may be used as a research reference book or as a textbook for senior undergraduate students or ?rst-year graduate students. The lectures for an one-semester or one-quarter course on guided waves along surface wave structures can begin with a review of EM fundamentals (Chap. 2), and then move on to a discussion on the general important and relevant characteristics of these guided surface waves (Chap. 3). Then follows the rigorous analytic treatment for canonical structures (planar, circular, and elliptical) (Chaps. 4–8). By the end of these lectures, the students would have gained a very solid theoretical fo- dation on this subject. Then the fun part starts.