Sishtla Sreeramamurthy Janaki, popularly known as S. Janaki, is an Indian playback singer and occasional music-composer from Andhra Pradesh. She is one of the best-known playback singers in South India and has recorded 48,000 songs in 17 Languages like Kannada, Malayalam, Tamil, Telugu, Odiya, Hindi, Bengali, Tulu, Sanskrit, Sinhalese, Badaga, Punjabi, Urdu, Japanese, German, Latin and Arabic languages. Starting in 1957, her career has spanned six decades. She has recorded songs in more than 17 regional Indian languages and foreign languages. She has won four National Film Awards and 33 different State Film Awards. Her association with singer S. P. Balasubrahmanyam and composer Ilaiyaraaja is well known. In the 1960s, 1970s and 1980s her duets with P. B. Srinivas, S.P.Balasubramanyam and with Dr. Rajkumar were some of the most romantic duets in the history of Tamil and Kannada film music.

S. Janaki, who is known as "The Nightingale of the South", is a recipient of an honorary doctorate from the University of Mysore and the Kalaimamani award from Tamil Nadu State Government.

In 2013, she refused the offer of a Padma Bhushan award by the Government of India, saying that it had come "too late" and that South Indian artists were not given their due recognition.

A book titled Aalpanathile Thenum Vayambum, authored by Abhilash Pudukad, details the life and career of Janaki.