As one reviewer has pointed out, you could make the mistake of buying this book thinking that it is a guide to learning to fly gliders. It is not, other books do that.
This book could be called "The Physics of Flying". It takes you through various aspects of flying: lift, drag, stalling,instruments; and explains in detail what is happening from a scientific perspective.
It is perfectly possible to learn to fly without knowing a lot of this - but I have found that knowing these things has made learning to fly a glider quicker and more interesting.
By using very clear diagrams, rather than pictures, Longland explains things step by step and treats the reader as an intelligent person, but one prepared to make some effort to understand. It is neither "dumbed down" nor submerged in technical jargon.
It is a book I shall have on the shelf and refer to for years to come.