Iyengar yoga is Hatha yoga. It is based upon the eight limbs of yoga (yamas, niyamas, asanas, pranayama, pratyahara, dharana, dhyana, and samadhi) set forth in Pantanjali’s Yoga Sutras, and expands upon this ancient practice. Iyengar adapted Hatha yoga to modern scientific disciplines such as anatomy, physiology, and psychology, and he developed the use of props, such as belts, bolsters, blocks, and blankets, as aids in performing asanas correctly, minimising the risk of injury and making the postures accessible to both young and old.
Iyengar yoga emphasizes the development of strength, stability, mobility, and precision in asanas (poses). Iynegar yoga is characterized by great attention to detail and on the structural alignment of the body in asana. These alignments seek to create space, and within this space the freedom to develop precision. This precision is used to unite the body, mind and spirit for health, well-being and union with God. Consider this incisive explanation of how it is practiced:
The first step is to train the mind to be passive in order to develop and use the intelligence of the body. …Then work on bringing the mind into and out of the pose, using reflection to make subtle corrections and then making the mind passive again. In this manner you let the body do what it has already learned, while intruding now and then with the mind to help the body learn more. …The brain relaxes and more efficiently receives knowledge from the body and guides the body to further refinements in action. Soon you are able to pause and reflect between each movement effortlessly as you move to and retain each pose. The, in the stillness you become filled with awareness. 
The use of "props" allows beginers to experience asanas more easily and fully than might otherwise be possible without several years of practice, and also allows tired or ill practitioners to enjoy the benefits of many asanas by supporting the body and its limbs. Iyengar also developed extensive ways of applying his practice to various ailments, diseases, and disorders. Many of these sources of suffering, such as chronic backache, immunodeficiency, high blood pressure, insomnia, depression and menopause, have specific programs of Iyengar yoga associated with them.
Iyengar’s emphasis on form and precision in asana and his extensive inventions of props has received a great deal of attention and praise. Sometimes overlooked, however, is the tremendous advances Iyengar has made in practicing and explaining the relationship between the use of breath in yoga to deepen mental and spiritual experience and skills:
To discover the individual soul you need inspiration—the creative force of breathing in. To discover the Cosmic Soul you need the courage to release, to breathe out, to make the ultimate surrender. Do not be discouraged. The Divine Will impels humankind to this end. Hold the soul (atman), not just the breath. There is a space between surrender and acceptance. You surrender to the Lord, and the Lord accepts your surrender. And, to accept, time and space are needed. That is retention (kumbhaka ). 
Iyengar has, more than ever before, divined and explained that final internal spiritual battle to which the authors of the Bhagavad Gita devoted 18 chapters:
Before our consciousness finally gravitates to our Self and our Self is merged in the Infinite, there are many fine threads to be woven together into the shimmering cloth of our practice. We have to weave in a meditation of such selfless purity that the impersonating ego will be unmasked for all time. When the ego is effaced, the afflictions that accompany it will disappear. 
Iyengar’s cues for how to attempt this in savasana —corpse pose—are particularly suggestive:
By becoming nobody and nothing we become small enough small enough to pass through an infinitesimally small crack in the curtain of time. A practitioner who can put aside his every identity can access places where no plump ego could squeeze through. …The ultimate yogic triumph is to live in kaivalya (God’s kingdom), outside time, you might say, but really inside it, inside its heart, disconnected from the past and from future. That is to live in the kernel of the present. It is the integration of the true nature of time in consciousness, and Savasana is the key. 
Iyengar’s work Light on Yoga has long been referred to as the “bible” for yoga asanas, but he has written many path-breaking works such as Light on the Yoga Sutras of Pantanjali andLight on Pranayama . He is currently working on more important books that we will soon see, but his Magnum opus is Light on Life, a work that every serious yoga practitioner—especially yoga teachers—should have close at hand.
For more information on Iyengar and Meditation see the meditation page: Meditation Techniques
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 BKS Iyengar, Light on Life (USA: Rodale, 2005), p. 31.
 BKS Iyengar, Light on Life (USA: Rodale, 2005), p. 201.
 BKS Iyengar, Light on Life (USA: Rodale, 2005), p. 202.
 BKS Iyengar, Light on Life (USA: Rodale, 2005), p. 235.