Originated in India 5,000 or more years ago, to the Aryan civilization in the Indus Valley . The Classical Yoga written by Patanjali , around in 500 BC , Yoga Sutras to explain the process and systematic analysis of practical methods for awakening and expanding the higher faculties of mind, intellect, quality of consciousness. His path of Ashtanga yoga included yamas and niyamas, Asanas, Pranayama, Pratyahara, Dharana, Dhyan, Samadhi. Yoga Sutras are concisely packed 196 lines in Sanskrit which are divided into 4 chapters.
The word 'Yoga' is derived from the Sanskrit root 'Yuj', meaning 'to join' or 'to yoke' or 'to unite'. As per Yogic scriptures the practice of Yoga leads to the union of individual consciousness with that of the Universal Consciousness, indicating a perfect harmony between the mind and body, Man & Nature.Thus the aim of Yoga is Self-realization, to overcome all kinds of sufferings leading to 'the state of liberation' (Moksha) or 'freedom' (Kaivalya)

Brief history of Yoga -

1- "Yoga is a light, which once lit, will never dim. The better your practice, the brighter the flame - –B.K.S lyengar
Yoga works on the level of one's body, mind, emotion and energy. Yoga does not adhere to any particular religion, belief system or community; it has always been approached as a technology for inner wellbeing This has given rise to four broad classifications of Yoga:
karma yoga, where we utilize the body;
bhakti yoga, where we utilize the emotions;
gyana yoga, where we utilize the mind and intellect; and kriya yoga, where we utilize the energy.
2- Traditional Schools of Yoga :
These different Philosophies, Traditions, lineages and Guru-shishya paramparas of Yoga lead to the emergence of different traditional schools of Yoga e.g. Jnana-yoga, Bhakti-yoga, Karma-yoga, Dhyana-yoga, Patanjala-yoga, Kundalini-yoga, Hatha-yoga, Mantra-yoga, Laya-yoga, Raja-yoga, Jain-yoga, Bouddha-yoga etc. Each school has its own principles and practices leading to ultimate aim and objectives of Yoga.
Why world needs Yoga ( On International Yoga Day) - by Sadhguru

Yoga for All – ( Significance of Namaskar )

"Yoga is the journey of the self, through the self, to the self." - The Bhagavad Gita
Yogic exercises recharge the body with cosmic energy and facilitates:
Attainment of perfect equilibrium and harmony
Promotes self- healing.
Negative energy is substituted by positive and vibrant energy .
Enhances personal power and self confidence .
Increases self-awareness
Meditation relaxes the mind and helps in attention, focus and concentration.
Rejuvenate the body cells and stimulates the active cells .
Reduces stress and tension in the physical body by activating the parasympathetic nervous system.
It reduces the risk of heart attack , improves the oxygenated blood circulated in body, by lowering the blood pressure risk .

"Yoga is an invaluable gift of India's ancient tradition. This tradition is 5000 years old. It embodies unity of mind and body; thought and action; restraint and fulfilment; harmony between man and nature; a holistic approach to health and well-being. It is not about exercise but to discover the sense of oneness with yourself, the world and the nature. By changing our lifestyle and creating consciousness, it can help in well being . Let us work towards adopting an International Yoga Day." — Narendra Modi, UN General Assembly, September 2014.
Watch out Yoga benefits , narrated by Sri Sri Ravi Shankar on India Today

Watch out Yoga lessons given on – ' Yoga with Modi '