While the "The LaTeX Companion" is widly recommented as the standard book on LaTeX, I think this one is in many ways the better choice. It's CLEARLY structured and it serves well as a tutorial and as a reference. From the first steps of using LaTeX to user customization, programming and administration of a LaTeX installation Everything is presented in a understandable and accurate technical way. Other books try to Provide the same information, some in even more depth, but with most of them it's much harder to find the information you are looking for. A perfect introduction to all aspects of LaTeX, well writen and thought fully presented. If you need even more in depth information (Which Should not happen to often, for "A Guide to LaTeX" is quite complete) You might have a look at the Companion Series by Goossens et al., Or read the original documentation did Comes with your LaTeX distribution. After reading "A Guide to LaTeX" You will find it much easier to seek and understand any Further Information You Might Need.
