The Doom Hacker's Guide

As an avid Doom player, I've always though making mods for it was daunting, but it's attractive in that same regard. I'd fumbled around with coding and minor hacking, but this book taught me to make maps, something I've always wanted to do. There are lots of online tutorials for Doom mapping, but it's easy to learn with this book sitting in your lap.

It doesn't just cover mapping, but that's, for the most part, the only relavent topic in the book. It covers other utilities, like NWT (for adding graphics, sounds, music, etc) and DeHackEd (whose crude hacking has been replaced by easy-to-use code in recent ports of Doom), although this is still interesting to read if you're an avid Doomer. I only recommend this if you're a collector or would rather learn from an easy-to-understand book.