Yoga may be a relatively new fitness trend in the West, but the beginnings of this very ancient practice can be traced as far back as the Indus-Sarasvati civilization, in Northern India more than 5,000 years ago. As a matter of fact, the first mention of the term “yoga” was in the oldest sacred texts known as the Rig Vega: one of a collection of “Vedas” containing mantras, rituals, and songs to be used specifically by Brahman Vedic priests.
Of course, that is the earliest evidence we can find, today. Some experts argue that yoga may date back in time even further; we just don’t have any evidence. This could be due to the fact that the earliest writings of yoga would have been transcribed on very fragile palm leaves; a material easily damaged and would have eroded with time (without proper preservation). Indeed, some researchers argue that yoga may be even 10,000 years old. 
PRE-CLASSICAL YOGA
This earliest time period—that we can trace (5,000 years ago)–is known as the pre-classical yoga stage. At this time, yoga was more of a hodgepodge of several ideas, beliefs, and fundamental teachings than the full system of poses and breathing techniques that we know of today. Of course, the practice began to go through a refining period and was eventually recorded into Yogic scriptures.
CLASSICAL YOGA
The beginning of Yoga’s Classical period is most often ascribed to the first systematic presentation of the system by Patanjali’s Yoga-Sûtras, around the second century. This text describes what is known as “Raja Yoga” or “Classical yoga;” organized into an “eight limbed path” with a series of steps and stages to follow and progress through in order to obtain Samadhi (enlightenment).
POST-CLASSICAL YOGA
Centuries after the introduction of the Raja Yoga, masters of the system began to evolve the practice into new systems specifically aimed at rejuvenation and prolonged life. This period actually rejects ancient Veda principles in favor of embracing the physical body to achieve Samadhi. This period is responsible, then, for Tantra Yoga, which introduces radical techniques for cleansing the body and mind and simultaneously breaks the bonds that tie us to the physical plane.
MODERN YOGA
Somewhere in the late 1800s yoga masters began to travel across the globe. Of course, this is when the rest of the world was introduced to yoga, and it started to grow into the Euro-spa yoga retreat craze that it is today.