From the Iyengar Yoga National Association of the United States: Yoga is for everyone. No one is too old or too stiff, too fat or thin or tired. A Certified Iyengar Yoga teacher can guide students of all ages and physical conditions to an experience of yoga, which is safe, accessible and rewarding.
Certified Iyengar Yoga instructors are held to an unusually rigorous standard. Only after years of training and evaluation do they become certified. Iyengar Yoga teachers modify the classic asanas (yoga postures) for individual students with the use of props -- such as blocks, blankets and belts. Props allow for a deeper penetration into the posture, as well as a longer stay.