Hatha Yoga is an important Yoga type. Hatha Yoga is an easy form of Yoga and is very popular in the United States and other western countries. Hatha Yoga is said to be the basis of all Yoga systems. The word Hatha is made of two words, "Ha" and "Tha", Ha means "sun" and "Tha" means "moon." Thus, Hatha Yoga refers to positive (sun) and to negative (moon) currents in the system.

This is perhaps a comparatively later development among the varieties of yoga. It is made of four parts, namely, Asana, Pranayama, Mudra and NadanusandhmlG. Swatmarama, an old authority on this yoga, declares in the Hathayoga-Pradipika, that Hatha Yoga is the staircase which leads a sincere student ultimately to the goal of Raja Yoga. It is supposed that a practice of the techniques included in this yoga brings about a union of what are called the sun and the moon in our body. The moon is situated in a region above the hard palate, and is believed to exude a fluid which percolates down, and is swallowed by the sun, which is situated near the navel. It is due to the swallowing up of this elixir by the sun, that we are said to suffer from old age and death. Hatha Yoga, in short, is a way of tackling these two, i.e. the sun and the moon in our body, so as to bring about a union of them.

Asanas, which form the first part of Hatha Yoga, bring about bodily and mental stability, which is a mark of perfect health. They make the body active and supple, by removing the impurities and extra fat.

The next two parts, namely Mudra and Pranayama, are aimed at making the breath silent, thereby activating certain dormant areas of our nervous system, when the nerves are completely divested of all impurities. This is spoken of in yogic terms as the arousal of the Kundalini, the divine power that usually lies dormant in human beings. We shall have occasion to discuss the notion of the Kundalini in detail while dealing with the techniques of the Mudras and Pranayama. The fourth part of Hatha Yoga, which is supposed to be the result of an intense and prolonged practice of the first three parts, is associated with concentrating the mind on the subtle sounds (nada) which an advanced student of yoga can hear after arousal of the Kundalini. This phenomenon continues for a while, and the student hears progressively subtler sounds until at least the nada becomes silent, making the mind completely absorbed in itself. This state is described by words like samadhi, sahajavastha, unmani, etc., and is the highest state of happiness that remains ever undisturbed by whatever happens in one's life. Such a person may rightly be said to have reached the goal of yoga that is common to all the varieties of yoga. It is indeed the state of liberation in bodily existence.

We shall here try to describe this state at some length, with a view to make two points clear, namely, what yoga really stands for, and who can be considered a real yogi. A student of yoga should understand these two points very clearly. A lot of confusion seems to prevail among the minds of many people, on these two points. We are obviously not referring here to people, who, with their long grown beards and hair, move about in the masses as masters of yoga, trying to impress people with demonstrations of unusual powers concerning bending metal bars, breaking thick metal plates, stopping moving cars, or walking on fire or water. Patanjali has mentioned many yogic powers or siddhis in the third chapter of the Yaga Sutra. But he has clearly warned the students of yoga against an unwise use and exhibition of them, by declaring that they are actually distractions in the path of samadhi.

A yogi, to be sure, is a person who behaves in everyday life like other persons. He has his biological needs; he has to eat and drink in order to keep the body living. But on the psychological plane his behaviour shows a vast difference. He is not motivated in the same fashion as most of us are. He has nothing to attain in the world for himself. Yet, he keeps on working for the good of humanity. His sense organs do work like those of others, but he is not swayed away by the sensations, nor does his mind run after objects of enjoyment. Jnaneshwara, the great master of yoga, has described the behaviour of a yogi in a very interesting manner as follows:

"The yogi may apparently respond to experiences in life, but he remains unaffected or undisturbed from within. Just as the moon responds to moonlight or the ocean responds to showers of rain, the yogi reacts passively to whatever confronts him in life. His choicelessness, passivity and peace are never disturbed by whatever he does, and while his sense organs behave in their usual manner, his silent samadhi remains ever undisturbed with all that he does".