How is tantra related to yoga? Yoga is well known, yet tantra is surrounded and veiled in an aura of superstition and mystery. This in a way is very strange, for in fact yoga and tantra are in essence the same system. They are intimately related. To be more specific: yoga is a part of the more encompassing, wider system of tantra. All practices such as asanas, pranayama, all yogic paths such as karma yoga, bhakti yoga, kundalini yoga, hatha yoga, mantra yoga, kriya yoga and so on, are all an integral part of tantra. All the practices that you know as yoga are also part of tantra. You have already been practising tantra and you have not known it!
Some people say that the science of yoga originated from Samkhya philosophy, but this is not really true. Yoga as it is widely known and practised, the yoga that has been practised in India for thousands of years, comes directly from tantra. Even Samkhya, which is a wonderful system of classifying the material world as a means to enlightenment (a way of jnana yoga to be more specific) is an integral part of certain sections of tantra, namely Kashmir Shaivism. In a wider sense, yoga has its roots in all religious systems, whether the path of the Vedas, Christianity, Buddhism or whatever. Yoga is an integral part of all religions. But the classified system of yoga as you know it, the form of yoga that originated, developed and flourished in the rich environment of India, comes almost completely from tantra. All the practices in this book are basically tantric.
To sum up: tantra covers a vast range of interests, from rituals to rules of regulating one’s life, from astrology to ayurvedic medicine. Yoga on the other hand is more specific; it is in general concerned with directly influencing the mind and body as a method of attaining good health, mental peace and eventually higher awareness. Tantra has the same aim, but it includes within its fold a greater range of methods and interests. We can say: tantra is the mother and yoga is the son.