The Hatha Yoga Pradipika is a classical text describing Hatha Yoga. It is said to be the oldest surviving text on Hatha Yoga. Swami Swatmarama, a disciple of Swami Goraknath, wrote the text in the 15th century CE, drawing upon previous texts and his own experiences.
While the text describes asanas (postures), purifying practices (shatkarma), mudras (finger and hand positions), bandhas (locks), and pranayama (breath exercises), it also explains that the purpose of Hatha Yoga is the awakening of kundalini (subtle energy), advancement to Raja Yoga, and the experience of deep meditative absorption known as samadhi.
From the Wikipedia:
The Haṭha Yoga Pradīpikā (Sanskrit:haṭhayōgapradīpikā, हठयोगप्रदीपिका) is a classic Sanskrit manual on hatha yoga, written by Svāmi Svātmārāma, a disciple of Swami Gorakhnath. Said to be the oldest surviving text on the hatha yoga, it is one of the three classic texts of hatha yoga, the other two being the Gheranda Samhita and the ShivaSamhita. A fourth major text, written at a later date by Srinivasabhatta Mahayogaindra, is the Hatharatnavali.
Its titles in the A.C. Woolner collection are described by the Library of the University of Vienna asHaṭhayogapradīpikā, Haṭhapradīpikā, Haṭhapradī, Hath-Pradipika.(source)
The text was written in 15th century CE. The work is derived from older Sanskrit texts and Swami Svatmarama’s own yogic experiences. Many modern English translations of the text are available.
The book consists four Upadeśas (chapters) which include information about asanas, pranayama, chakras, kundalini, bandhas, kriyas, shakti, nadis and mudras among other topics. It runs in the line of Hindu yoga (to distinguish from Buddhist and Jain yoga) and is dedicated to Śrī (Lord) ādi nāthā (Adinatha), a name for Lord Shiva (the Hindu god of destruction and renewal), who is believed to have imparted the secret of hatha yoga to his divine consort Parvati.