Nagas are one of the most prominent mythological beings mentioned in the Hindu scriptures. They are supernatural serpents in Hindu mythology and are depicted as either complete serpents, complete humans with multiple snake hoods emerging from their back, beings with half-snake and half-human body, and some having the ability to shapeshift between these forms. They are said to live in Patal Lok, an aquatic realm under the surface of the earth that is filled with treasures, unimaginable to humankind, and anthills are often considered as holy portals to this semi-divine underworld. Apart from that underworld, Nagas also dwell in other water bodies like lakes, rivers and oceans. These divine creatures with mystical powers are synonymous with nature spirits and are a symbol of rebirth, death, fertility, immortality, medicine, health and wealth. Due to this, snake worship has been a practice in India since ancient times. An iconic festival dedicated to snakes is Nag Panchmi. People all over the country offer their prayers to these nature spirits as a part of the celebrations.

According to Mahabharata, rishi Kashyap and Kadru, daughter of Daksh, are the parents of all nagas. Out of them, Shesha was the eldest, and then came Vasuki, Manasa, and many others. Kashyapa had another wife, who was also Kadru’s sister, Vinata. She gave birth to Vishnu’s vahana, Garuda, an eagle-human hybrid and he became the arch-nemesis of the nagas since eagles consume snakes. In the Ramayana, Indrajit used the Nagapasha astra on Rama and Lakshmana, which hurled venomous snakes over them. The two fell unconscious and Garuda came to their rescue. He got rid of the venomous snakes. There are various stories of enmity between Garuda and nagas in the scriptures, which depict the aggressive nature of the nagas. But on the contrary, there are also some nagas that are mentioned in the scriptures for their good deeds, in both Vaishnavism and Shaivism.

In various Asian religious traditions, the Nagas (Sanskrit: नाग, romanized: Nāga) are a divine, or semi-divine, race of half-human, half-serpent beings that reside in the netherworld (Patala), and can occasionally take human or part-human form, or are so depicted in art. A female naga is called a Nagi, or a Nagini. Their descendents are known as Nagavanshi and Nair. According to legend, they are the children of the sage Kashyapa and Kadru. Rituals devoted to these supernatural beings have been taking place throughout South Asia for at least 2,000 years. They are principally depicted in three forms: as entirely human with snakes on the heads and necks, as common serpents, or as half-human, half-snake beings in Hinduism, Buddhism, and Jainism.

Nagaraja is the title given to the king of the nagas. Narratives of these beings hold cultural significance in the mythological traditions of many South Asian and Southeast Asian cultures, and within Hinduism and Buddhism. Communities such as the Nagavanshi, Nair, Khmer and Eelamese claim descent from this race.

In Sanskrit, a nāgá (नाग) is a snake, most often depicted by a cobra, the Indian cobra (Naga Raja). A synonym for nāgá is phaṇin (फणिन्). There are several words for "snake" in general, and one of the very commonly used ones is sarpá (सर्प). Sometimes the word nāgá is also used generically to mean "snake". The word is cognate with English 'snake', Germanic: *snēk-a-, Proto-IE: *(s)nēg-o- (with s-mobile).

Alternatively, an Indo-European etymology as a “hairless, naked animal” - cognate to English "naked" - would explain that the Sanskrit word nāga can also mean “cloud”, “mountain” or “elephant”.

Nagas as a serpent-shaped group of deities that often take form as cobras are prominent in Hindu iconography, throughout the mythology (especially in the first book of the Mahābhārata) and in local folk traditions of worship. In some regions of the Himalaya, nagas are regarded as the divine rulers of the region - as in Kullu Valley, in Berinag and in the valley of the Pindar River, which is believed to be ruled by the ninefold Naiṇī Devī. Both in the Nilamata Purana of Kashmir and in the Swayambhu Purana of Kathmandu, the respective region begins its history as a lake, populated by nagas, which is later drained.

Mythological Sanskrit texts such as the Mahabharata,the Ramayana and the Puranas describe the nagas as a powerful, splendid and proud semi-divine species that can assume their physical form either as human (often with a halo of cobra hoods behind their head), as a partially human serpent, or as a whole serpent. Their domain is in the enchanted underworld, the underground realm filled with gems, gold and other earthly treasures called Naga-loka or Patala-loka. They are also often associated with bodies of waters — including rivers, lakes, seas, and wells — and are guardians of treasure. Their power and venom made them potentially dangerous to humans. However, in Hindu mythology, they often take the role of benevolent protagonists; in the Samudra Manthana, Vasuki, a nagaraja who abides on Shiva's neck, became the churning rope for churning of the Ocean of Milk. Their eternal mortal foe is the Garuḍa, the legendary semi-divine bird-like deity.

Vishnu is originally portrayed in the form sheltered by Sheshanāga or reclining on Shesha, but the iconography has been extended to other deities as well. The serpent is a common feature in Ganesha iconography, and appears in many forms: around the neck, use as a sacred thread (Sanskrit: yajñyopavīta) wrapped around the stomach as a belt, held in a hand, coiled at the ankles, or as a throne. Shiva is often shown garlanded with a snake. Maehle (2006: p. 297) states that "Patanjali is thought to be a manifestation of the serpent of eternity".

The names of the 9 Naag Devatas are Ananta, Vasuki, Shesha, Padmanabh, Kambal, Shankhapal, Dhrutrashtra, Takshaka and Kalia. Also known as Nav Naga Stotram, this powerful mantra of the nine nagas can be chanted on Nag Panchami, Naga Chaturthi and Shasti days.

The Divine Nāgas, who can travel to heaven, came from Lord Indra's realm (the divine realm). They can take on a full human form. The Supreme and Divine Nāgas, like Vasuki the follower of Lord Shiva, who alone can fight the entire Garuḍa race.

Kadru is known as the mother of the nagas, the race of serpents. The Nāgas: Sons: Kaliya, Takshaka, Shesha, Vasuki, Karkotaka etc. Legends of Kadru detail her relationship with her elder sister Vinata, who was also one of Kashyapa's many wives.

The snake primarily represents rebirth, death and mortality, due to its casting of its skin and being symbolically "reborn". Over a large part of India, there are carved representations of cobras or nagas or stones as substitutes. To these human food and flowers are offered and lights are burned before the shrines.

The Mahabharata epic is the first text that introduces nagas, describes them in detail and narrates their stories. The cosmic snake Shesha, the nagarajas (naga kings) Vasuki, Takshaka, Airavata and Karkotaka, and the princess Ulupi, are all depicted in the Mahabharata.

The Brahma Purana describes the reign of Adishesha as the king of the serpents in Patala:

During the night the light of the moon is not utilised for its coolness but only for illumination.

Since that passes away is not taken notice of by the Nāgas who enjoy with gaiety the foodstuffs and the edibles they consume and the great beverages they drink. Nor are Danujas and others aware of it.

O brahmins, the forests, rivers, lakes, and lotus ponds, the cooing of the cuckoo and other sweet birds, the pleasing skies, the unguents and the continuous notes and sounds of musical instruments such as the lute, flute and Mṛdaṅga drums, O brahmins—all these and other beautiful things are enjoyed by virtue of their good luck by Dānavas, Daityas and Nāgas residing in Pātāla. The Tāmasī form of Viṣṇu, named Śeṣa is beneath the lower regions.

Daityas and Dānavas are not capable of recounting his good qualities. He is honoured by Devas and celestial sages. He is spoken of as Ananta. He has a thousand hoods and he is clearly bedecked in Svastika ornaments devoid of impurities. He illuminates all quarters by thousand jewels on his hoods.

— Brahma Purana, Chapter 19

The Kamba Ramayana describes the role of Vasuki in the Samudra Manthana:

The devas and the asuras decided to get Amṛta (Ambrosia—the celestial honey of immortalily) by churning the sea of milk. The Devas went to bring Mandara-mountain, to be used as the churning rod. Their attempt was futile. The asuras made a trial with the same result. The Bhūtagaṇas (Guards) of Śiva also made a vain attempt. On the instruction of Viṣṇu, Garuḍa went and brought the mountain as easily as an eagle takes away a frog. Now Vāsuki should be brought. The Devas and Gandharvas failed in that attempt also. Garuḍa who was haughty of his strength and speed, went to the city of the nāgas (serpents) and requested Vāsuki to come to the sea of Milk. Vāsuki replied that if the matter was so urgent he had no objection for being carried to that place. He took the middle part of Vāsuki in his beak and flew up higher and higher and reached beyond the horizon. Still the lower half of Vāsuki was lying on the ground. So he took Vāsuki in his beak as folded in two. Still the result was the same. Garuḍa became aware of the impossibility of carrying Vāsuki and returned, ashamed and disappointed. Viṣṇu rebuked him for his arrogance. After this, Śiva stretched his hand to Pātāla. Vāsuki became a small bangle on that hand. Thus Vāsuki was brought to the shore of the sea of Milk.

— Kambar, Ramayana, Yuddha Kanda

The Devi Bhagavata Purana describes the legend of Manasa:

Manasā is the mind-born daughter of Maharṣi Kaśyapa; hence she is named Manasā; or it may be She who plays with the mind is Manasā. Or it may be She who meditates on God with her mind and gets rapture in Her meditation of God is named Manasā. She finds pleasure in Her Own Self, the great devotee of Viṣṇu, a Siddha Yoginī. For three Yugas She worshipped Śrī Kṛṣṇa and then She became a Siddha Yoginī. Śrī Kṛṣṇa, the Lord of the Gopīs, seeing the body of Manasā lean and thin due to austerities, or seeing her worn out like the Muni Jarat Kāru called her by the name of Jarat Kāru. Hence Her name has come also to be Jarat Kāru. Kṛṣṇa, the Ocean of Mercy, gave her out of kindness, Her desired boon; She worshipped Him and Śrī Kṛṣṇa also worshipped Her. Devī Manasā is known in the Heavens, in the abode of the Nāgas (serpents), in earth, in Brahmāloka, in all the worlds as of very fair colour, beautiful and charming. She is named Jagad Gaurī as she is of a very fair colour in the world. Her other name is Śaivī and she is the disciple of Śiva. She is named Vaiṣṇavī as she is greatly devoted to Viṣṇu. She saved the Nāgas in the Snake Sacrifice performed by Pariksit, she is named Nageśvarī and Nāga Bhaginī and She is capable to destroy the effects of poison. She is called Viṣahari. She got the Siddha yoga from Mahādeva; hence She is named Siddha Yoginī

— Devi Bhagavata Purana, Chapter 47