In Hindu mythology, Devayani (Sanskrit: देवयानी, Devayānī) was the important daughter of Shukracharya, Daitya guru and his wife Jayanti, daughter of Indra. She was married to Yayati, and gave birth to two sons — Yadu and Turvasu.
Kacha, son of Brihaspati (Guru of Devas) was sent to the Shukracharya to learn the Mrita Sanjivini Mantra (technique of bringing dead back to life). His father tells him to impress Devayani, dearest daughter of Shukracharya in order to get the blessings of Shukracharya. Kacha follows his advice and unknown to him Devayani falls in love with him. Shukracharya's Daitya disciples want to kill Kacha as he was the son of their rival and could do them harm if he learns Mrita Sanjivini Mantra. They try to kill him twice but Shukracharya brings him back to life on Devayani's insistence. At last they burn him, mix that ash in alcohol and give that to Shukracharya. Shukracharya realises that later and he teaches Mrita Sanjivini Mantra to Kacha and asks him to come out of his stomach by killing him. Kacha comes out and brings Shukracharya back to life with the help of Mantra.
Sharmishtha was the daughter of Vrisaparva, the Danava king, for whom Shukracharya was an adviser. One day Sharmishtha, daughter of the Danava king Vrishparva and Devayani, daughter of the Daitya sage Shukracharya, go with Sharmishtha's retinue to bathe in a forest pool not far from their home. After bathing, Sharmishtha confuses Devayani's sari with hers and puts it on instead. Devayani returns, scolds Sharmishtha for her mistake and belittles her with the jibe that she is the daughter of Shukracharya (Shukracharya being a sage and high priest and indeed the guru of all the Asuras - no mere employee) as Vrishparva's and their Kingdom lives on his blessings. This slur on herself and her father Vrishparva infuriates Sharmishtha with the help of her servants throws the naked Devayani into a well and leaves the forest with her retinue. Later Yayati, son of Nahusha, comes to the well for water and helps Devayani to climb out of it. When Devyani comes back to her father, she narrates the whole story and demands that Sharmishtha along with other asura girls serve her as maid, which Vrishparva has to agree for he doesn't want to offend Shukracharya.
Some days later Devayani goes to a picnic in the forest along with her Sharmișțha and other servants. There Yayati comes for hunting and they meet again. This time she brings him to her father and tells him that they would like to marry. Shukracharya gives his consent and tells Yayati that he should take care of Sharmista too as she was a princess but shouldn't have nuptial relation with her. Yayati marries Devayani and looks after her well.
Yayati sired two sons, Yadu and Thurvasu with Devyani. Unknown to her he had three sons with Sharmista, Dhruhyu, Anu and Puru. When Devayani learns of this she leaves him and returns to her father's place. Shukracharya curses him with premature old age. However, on Yayati's insistence he agrees to reduce the curse on condition that Yayati can swap his old age with the youth of any of his young sons. Yayati swaps his youth with his 5th son Puru. 
After enjoying some time, Yayati gives his youth back to his son along with his kingdom. Devayani and Yayati leave for forest to spend time peacefully and engage in religious activities dictated as per Dharma. They die there after some time. Her son Yadu gives rise to Yadu dynasty in which Krishna was born later.