As the author of several books concerned with vacuum tube applications, I thought it might be helpful to provide an introduction to the theory of vacuum tubes. Reading such a book first might make the theory behind these applications more easily understood. In the spirit of my "From Scratch" books, I start with the basics, build the theory from these, and end with an application that applies the theory. As a place to start, what could be more basic than the electron itself? That, then, is the subject of Chapter 1. From there, I explore vacuum tube diodes, triodes, tetrodes, pentodes and heptodes. For each, I show an application that demonstrates the elements of the theory. As always in my "From Scratch" books, I make no assumptions about what you know about the subject. Math is occasionally involved in theory sections, but I keep it at the basic algebra level. On occasion, I use simulation to verify the theory. Finally, I put all the tube theory together in an AM radio that utilizes the tubes from the previous chapters. In short, I take the mystery out of vacuum tubes and bolster your confidence when taking on future tube application projects.