If you want to get Byron Katie, read this book first, not the others. Moreover, get the audio version, not the text. In text, she makes no sense and what sense she makes sounds frankly dangerous and irresponsible in places. The sample conversations on the audio version clarify things tremendously...they give you the ability to see (hear) what she's getting at and the purpose of these mental exercises. It makes more sense when you hear it in action.
This is very different than other books within the personal development genre. This book and "the work" described within will transform you.
OMG! The book is absolute GARBAGE! The cornerstone of this book is that pretty much nothing is real and that any and everything bad that someone else does to us really isn't bad and if it were bad it is really our fault. Byron Katie actually gets a woman who was repeatedly raped by her father to ask herself how SHE abused Father. Vile and despicable!
The Work is life changing and immediately applicable because of its simplicity. I'll never look at problems the same way again.
The best thing I've gained from this teaching are the lessons I receive every day from my wife and kids. The things they do used to drive me crazy until I was able to see myself in those actions. What really drives me crazy is that I am guilty of those same behaviors.
This is a book for anyone in pain that is sick and tired of struggling.
Listening instead of reading helped me digest her thoughts with much greater clarity.