Bahiranga and Antaranga Yoga

Ashtanaga Yoga as codified by Patanjali consists of eight limbs or branches and should be approached in a step by step manner. Swami Gitananda said that there can be no higher Yoga without the foundations of the lower yoga. A spiritual or Yogic life which has no moral or ethical foundation can not produce an evolutionary change in the student, which is the goal of Yoga.
The eight limbs of Ashtanga Yoga are: Bahiranga Yoga (the lower stages)

Yama - Morals
Niyama - Ethics
Asana - Posture
Pranayama - Breath Control

Antaranga Yoga (the higher stages)

Pratyahara - Control of the senses
Dharana - Concentration
Dhyana - Meditation
Samadhi - Enlightenment

The eight limbs are split into two categories: Bahiranga yoga (the lower practices) and Antaranga yoga (the higher practices). The preliminary stages of yoga are the foundations upon which the higher practices are firmly based upon.