Yama, Niyama, Asana, Pranayama, Pratyahara, Dharana, Dhyana, and Samadhi are the eight limbs
Yama—universal disciplines / control of our inner subtle processes / restraints, Niyama—internal disciplines / observances, Asana—posture, Pranayama—breath regulation / life energy control, Pratyahara—sense withdrawal, Dharana—concentration, Dhyana—Meditation, and Samadhi-cognitive /enstatic absorption are the eight limbs of Yoga.
The above constitute the eight limbs of Yoga, limbs signifying attachment to a body therefore the eight limbs constitute the body of Yoga philosophy and in order to understand and experience Yoga in its full and complete extent, from a holistic perspective the angas or limbs cannot be dissociated from one another.
As Dr Swami Gitananda Giri Maharaj quite cleverly explains: there is no Yoga without the Yamas and Niyamas (universal and internal disciplines as the bedrock of the psyche—i.e. the foundation ) and Yoga is a step-by-step process (to build the solid construction of the Tower of Consciousness that is Yoga). This is often under-emphasized in modern Yoga (especially in the West) and at times all together omitted.