This book rounds up and ties together all the books of Yogani's 'Enlightenement Series', a small set of short books which are possibly the best general treatment of yoga around.
The 'Enlightenment Series' are written largely for the purpose of self-directed spiritual practice, and can be incorporated into any spiritual discipline.
If you are a beginner in Yoga, these books are a great introduction, if you are experienced, they are a great review, and they would be helpful and clarifying also for those approaching yoga from a Religious Studies perspective.
'Eight Limbs of Yoga' ties all the other books together, and shows how all the practices of yoga belong to one whole. It also elaborates on 'self-pacing', which is important for the individual practicioner, practicing without a guru.
You can buy 'Eight Limbs of Yoga' alone and get a lot out of it. The best thing to do though is, I'd say, is to buy the whole set. They're great value! If you want to read my own recommendations on them individually, click on 'see all my reviews'.