Michael Quinion is in the business of dispelling language myths, as well as explaining etymologies and the meaning of common phrases and slang. He's being doing this for years on his excellent web site World Wide Words. This book is a distillation of some of the material that has appeared on his web site, in a simple A to Z format. It's thoughtful and well written, and explains lots of those irritating or puzzling terms and expressions ("cheap at half the price", "mind your Ps and Qs"). My one complaint is that it's printed on rather low quality paper. Otherwise very good, and I recommend the web site too, which has a whole lot more material on it.