This is one of the oldest of the relatively small niche of books about RPGs: Fantasy Role Playing Games (1981), by J. Eric Holmes, the same Holmes who shepherded the original Basic Set Dungeons & Dragons into existence.
In the early 80s, a bunch of these types of books came out; they were sort of introductions to the idea of RPGs, mixed with brief how-tos and overviews of the market. This is probably my favorite of the ones I have read. The first third or so of the book is an overview of the key concepts of how to play, complete with transcripts of game sessions and a sort of read-along dungeon. Holmes shines, though, when he gets to the history of Dungeons & Dragons, in which he was a firsthand eye witness for a time. The immediacy of his account is engrossing, even if he is an unabashed Gygax cheerleader.
He follows this with a look at other games on the market (including big ones like RuneQuest and Traveller, as well as odd ones like Bunnies & Burrows and Superhero 44), miniatures and the magazines (both the semi-pro stuff like Dragon and the zines like Alarums & Excursions). The brief chapter on computer games is a hoot and rightly spends a chunk of time on Zork. I quite like the photographs that use miniatures and simple FX to great effect.
I also particularly like the penultimate chapter, which discusses the supposed perils of roleplaying. It makes a spirited defense of the hobby and also muses on the sorts of people who are attracted to it. It is one of the earliest acknowledgments I’ve seen of the hobby’s gender disparity and Holmes has some thoughtful ideas on why that is. It is his hope, back in 1981, that parity will be attained when RPGs are more popular and socially accepted. Nearly 40 years later, I like to think it is moving in that direction.
(Repost from April 27, 2020; lightly revised)