Practicing postures is one of the eight limbs of classical Raja yoga, as described by Patanjali in the "Yoga Sutras." Although they are just one of the eight limbs, postures are the aspect of yoga that's most practiced in the West.
There are many different yoga postures that are meant to stimulate, strengthen and open different areas of the body. Many postures are believed to have profound healing and therapeutic value. It is said that postures have physical, mental and energetic benefits. They balance energy in the body, opening chakras and calming the mind. Performing postures can also help the practitioner become more mindful, developing both their concentration and their awareness of the body.
Different schools and traditions of yoga describe a different number of yoga postures. It is said that Lord Shiva taught 85 classical yoga postures, while Sivananda yoga teaches 12 basic postures. Other teachers and gurus have said that there are an infinite number of possible postures.