Hatha yoga (Sanskrit haṭha yoga), also known as Hatha vidya, is a particular system of Yoga introduced by Yogi Swatmarama, a sage of 15th century India, and compiler of the Hatha Yoga Pradipika. In this treatise Swatmarama introduces Hatha Yoga as 'a stairway to the heights of Raja Yoga', hence a preparatory stage of physical purification that renders the body fit for the practise of higher meditation. The Asanas and Pranayama in Raja Yoga were what the Hindu Yogis used to physically train their body for long periods of meditation. This practise is called shatkarma. The word Hatha is a compound of the words Ha and Tha meaning sun and moon and refers to the principal nadis (energy channels) of the subtle body that must be fully operational to attain a state of dhyana or samadhi. In other respects Hatha yoga follows the same principles as the Raja Yoga of Patanjali including moral restraint yama and spiritual observances niyama. Hatha Yoga is what most people in the West associate with the word "Yoga" and is practiced for mental and physical health throughout the West.

Traditional Hatha Yoga is a holistic yogic path, including moral disciplines, physical exercises (e.g., asanas (postures) and Pranayama (breath control)), and meditation. The Hatha yoga predominantly practiced in the West consists of mostly asanas (postures) and exercise.

Hatha Yoga is one of the two branches of Yoga that focus on the physical culture, the other one being Raja Yoga. Both of these are commonly referred to as Ashtanga Yoga, i.e., Yoga of eight parts ('ashta' meaning eight and 'anga' meaning limbs). The eight limbs are described below in detail. The main difference is that Raja Yoga uses asanas to mainly get the body ready for prolonged meditation, and hence focuses more on the meditative asana poses: Lotus Pose (Padmasana), Accomplished Pose (Siddhasana), Easy Pose (Sahajasana) and Pelvic Pose (Vajrasana); Hatha Yoga utilizes most of the asana poses. Similarly, Raja Yoga's use of Pranayama is also devoid of extensive locks (Bandha).

Hatha represents opposing energies: hot and cold (fire and water, following the same concept as the yin-yang), male and female, positive and negative. Hatha yoga attempts to balance mind and body via physical exercises, or "asanas", controlled breathing, and the calming of the mind through relaxation and meditation. Asanas teach poise, balance & strength and are practiced to improve the body's physical health and clear the mind in preparation for meditation in the pursuit of enlightenment.

The Yoga of Patanjali is Ashtanga or composed of 8 limbs, Yama and Niyama, which are ethical obligations, Asana, Pranayama, which is breath control, Pratyahara, which is sense withdrawal, Darana, which is concentration, Dhyana, which is meditation, and Samadhi, which is the experience of unity with God.[1]. The eight limbs are more precisely viewed as eight levels of progress, each level providing benefits in and of itself and also laying the foundation for the higher levels.

NOTE: In some schools of thought, only Raja Yoga is considered to be Ashtanga Yoga, and Hatha Yoga is thought to consist of six limbs focused on attaining Kundalini. In this scheme, the six limbs of Hatha Yoga are defined as Yama, Niyama, Asana, Pranayama, Mudra (specific postures to help lock in the breath), Nadanusandhana (hearing of the eternal sound within the body), the whole process cultiminating in the attainment of Kundalini. Due to this, this version of Hatha yoga is also sometimes referred to as Kundalini Yoga.