Hatha yoga (/ˈhʌtə, ˈhɑːtə/; Sanskrit हठयोग, IAST: haṭhayoga) is a branch of yoga that uses physical techniques to try to preserve and channel vital force or energy. The Sanskrit word हठ haṭha literally means "force", alluding to a system of physical techniques. Some hatha yoga style techniques can be traced back at least to the 1st-century CE, in texts such as the Hindu Sanskrit epics and Buddhism's Pali canon. The oldest dated text so far found to describe hatha yoga, the 11th-century Amṛtasiddhi, comes from a tantric Buddhist milieu. The oldest texts to use the terminology of hatha are also Vajrayana Buddhist. Hindu hatha yoga texts appear from the 11th century onward.

Some of the early hatha yoga texts (11th-13th c.) describe methods to raise and conserve bindu (vital force, that is, semen, and in women rajas – menstrual fluid). This was seen as the physical essence of life that was constantly dripping down from the head and being lost. Two early hatha yoga techniques sought to either physically reverse this process of dripping by using gravity to trap the bindhu in inverted postures like viparītakaraṇī, or force bindu upwards through the central channel by directing the breath flow into the centre channel using mudras (yogic seals, not to be confused with hand mudras, which are gestures).

Almost all hathayogic texts belong to the Nath siddhas, and the important early ones (11th-13th c.) are credited to Matsyendranatha and his disciple, Gorakhnath or Gorakshanath (11th c.). Early Nāth works teach a yoga based on raising kuṇḍalinī through energy channels and chakras, called Layayoga ("the yoga of dissolution"). However, other early Nāth texts like the Vivekamārtaṇḍa can be seen as co-opting the hatha yoga mudrās. Later Nāth as well as Śākta texts adopt the practices of hatha yoga mudras into a Saiva system, melding them with Layayoga methods, without mentioning bindu. These later texts promote a universalist yoga, available to all, "without the need for priestly intermediaries, ritual paraphernalia or sectarian initiations."

In the 20th century, a development of hatha yoga focusing particularly on asanas (the physical postures) became popular throughout the world as a form of physical exercise. This modern form of yoga is now widely known simply as "yoga".

According to the Indologist James Mallinson, some haṭha yoga style techniques practised only by ascetics can be traced back at least to the 1st-century CE, in texts such as the Sanskrit epics (Hinduism) and the Pali canon (Buddhism). The Pali canon contains three passages in which the Buddha describes pressing the tongue against the palate for the purposes of controlling hunger or the mind, depending on the passage. However, there is no mention of the tongue being inserted further back into the nasopharynx as in true khecarī mudrā. The Buddha also used a posture where pressure is put on the perineum with the heel, similar to modern postures used to stimulate Kundalini. In the Mahāsaccaka sutta (MN 36), the Buddha mentions how physical practices such as various meditations on holding one's breath did not help him "attain to greater excellence in noble knowledge and insight which transcends the human condition." After trying these, he then sought another path to enlightenment. The term haṭha yoga was first used in the c. 3rd century Bodhisattvabhūmi, the phrase na haṭhayogena, seemingly meaning only that the bodhisattva would get his qualities "not by force".

The earliest mentions of haṭha yoga as a specific set of techniques are from some seventeen Vajrayana Buddhist texts, mainly tantric works from the 8th century onwards. In Puṇḍarīka's c. 1030 Vimalaprabhā commentary on the Kālacakratantra, haṭha yoga is for the first time defined within the context of tantric sexual ritual:

when the undying moment does not arise because the breath is unrestrained [even] when the image is seen by means of withdrawal (pratyahara) and the other (auxiliaries of yoga, i.e. dhyana, pranayama, dharana, anusmrti and samadhi), then, having forcefully (hathena) made the breath flow in the central channel through the practice of nada, which is about to be explained, [the yogi] should attain the undying moment by restraining the bindu [i.e. semen] of the bodhicitta in the vajra [penis] when it is in the lotus of wisdom [vagina].

While the actual means of practice are not specified, the forcing of the breath into the central channel and the restraining of ejaculation are central features of later haṭha yoga practice texts.