Vamana (Sanskrit: वामन, lit. 'Dwarf', IAST: Vāmana), also known as Trivikrama (lit. 'three steps'), Urukrama (lit. 'far-stepping'), Upendra (lit. 'Indra’s younger brother/Superior to Indra'), Dadhivamana (Sanskrit: दधिवामन, lit. 'milk-dwarf', IAST: Dadhivāmana), Ulagalanthan (lit. 'the one who measured the world) and Balibandhana (lit. 'binder or killer of Bali'), is an avatar of the Hindu deity Vishnu. He is the fifth avatar of Vishnu and the first Dashavatara in the Treta Yuga, after Narasimha.

First mentioned in the Vedas, Vamana is most commonly associated in the Hindu epics and Puranas with the story of taking back the three worlds (collectively referred to as the Trailokya) from the daitya-king Mahabali by taking three steps to restore the cosmic order and push Mahabali into the netherworld. He is the youngest among the adityas, the sons of Aditi and the sage Kashyapa.

'Vāmana' (Sanskrit वामन) means 'dwarf', 'small' or 'small or short in stature'. It also means 'dwarfish bull', which is notable as Vishnu is directly associated with dwarfish animals (including bulls) in the Vedas (see below). Stated in Puranic literature to be born of the great sage Kashyapa and his wife Aditi, other names or epithets referring to Vamana include:

After Indra (the king of the devas and the son of Kashyapa and Aditi) was defeated by the daitya called Bali, the king of the asuras, the great-great grandson of Kashyapa and Diti, the devas ultimately seek refuge in Vishnu, who agrees to restore Indra to power. To do so, Vishnu incarnates as Vamana (the son of Kashyapa and Aditi )

Mahabali decided to perform a grand Ashwamedha Yagna (horse sacrifice ritual) at a place called Bhrigukachaka on the northern bank of the Narmada River.

Vamana arrived there, and asked for three feet (steps) of land (usually to build a fire-altar). Bali agreed, despite being warned about Vamana's true nature as Vishnu (usually by his preceptor, the sage Shukra, the son of Bhrigu).

Vamana grew as Trivikrama. With one foot, he measured the entire Earth and the underworld, Patala. With the other foot, he measured the sky and the heavens.

He looked at King Bali and asked where should the third step land. Determined to keep his word, King Bali told Vamana to place the third step on his head. Upon hearing this, Lord Vishnu appeared in his true form and blessed King Bali and allowed him to rule the underworld. So Bali went to Patala, the netherworld. Due to the Vamana incarnation of Lord Vishnu, Indra and other gods retained Amaravati.