Published yearly since the 1920s by the American Radio Relay League, this is a reference to the theory and practice of amateur radio. My copy's the 1977 edition. I'm not a radio ham, but I've got a keen interest in electronics from an audio and computing perspective, and there's plenty here that'll be of interest if you're into wireless networking, for example.
I was particularly impressed by the thorough introduction to electronics and radio theory; much like Horowitz and Hill, it's written clearly enough that it works as an introduction, but structured so that it can also be used as a quick reference. The book has clearly been drawn together from the work of multiple authors, and is therefore a bit variable in style, but the quality is generally high, and it does a good job of covering all the bases.
The modern equivalent of this book appears to be "The ARRL Handbook", so that's what the ISBN below is for; older editions are easy to find cheaply second-hand, though, and if you're just after the electronics and RF theory then I'd hunt down a 1990s edition.