To me the chakras have always been one of the mystical aspects of Yoga; even after more than 20 years of Yoga practise. This book explains and effectively de-mystifies it. Why? Because the author not only shares the theories of the Chakras but also tries to substantiate it with emperical evidence - both his own as well as experimental.
Apart from explaining the different energy centers (Chakras) in the body, a series of asanas and techniques are outlined to awaken each of them. The best part of the book is the personal experience of the author. In this he explains how each of his chakras were awakened and what impact it had in his life. This (and my own experience of awakening of 2 of the centres) helped me believe in the existence of the chakras.
Knowing about the chakras is essential for spiritual development. The chakras are energy centres within the three human bodies: the etheric physical, astral and mental. We ought to learn about these centres as their awakening and unfoldment will be part of every person's growth. (ie. There'll be a lifetime when the disciple or initiate is unable to ignore the chakras.) Chakras are doors to the higher realms, and keys to spiritual powers.
There are ancient texts from Eastern religions on this subject. Among the more modern accounts of this are three classical 20th century books: "The Serpent Power" (1918) by Arthur Avalon, "The Chakras" (1926) by CW Leadbeater and "Theories of the Chakras: Bridge to Higher Consciousness" (1981) by Hiroshi Motoyama. Motoyama's book covers the other two and presents yogic exercises as taught by Swami Satyananda. The exercises are postures (Asanas) designed to gradually and safely prepare the physical body for opening of the seven main chakras.
The chakras are all linked by energy flow lines throughout the body known as nadis. The nadis are also related to the so-called meridians, which were well known to acupuncturists for thousands of years in China. The meridians are also utilised in Shiatsu, or "Touch for Health" where pressure-points on the body are massaged or pressed. The study by Motoyama discusses the chakras':-
1. Locations in the body(or inner bodies),
2. Appearance, descriptions and symbolisms,
3. Qualities when opened or awakened.
In addition Motoyama devised electrical instruments to measure the comparative "charge" around chakras and through the nadis. This part of the book is a bit dry, however the overall text is significant.
The interesting part about the books on chakras is that each says the unfoldment of these centres is a precise science for the initiate. Understandably then, the books can only at best imply the techniques for awakening the chakras by leaving many gaps in the descriptions for the disciple to fill. Furthermore, there is always the sensible warning that wrong or premature awakening of chakras can lead to physical, emotional or mental illness or even death. Despite there being now a lot of chakra books around, I think Motoyama's account is the best starting point.