Sistla Sreeramamurthy Janaki (credited as S. Janaki) (born 23 April 1938) is an Indian playback singer, songwriter and occasional music composer who has predominantly worked in South Indian Cinema. Known for her voice modulation capabilities and versatility, she has been described in the media as one of the greatest and most influential singers in Telugu, Malayalam, Tamil and Kannada language films. In her career spanning over six decades, she has recorded songs for films and albums in various Indian languages and received several accolades including four National Film Awards, eleven Kerala State Film Awards, ten Andhra Pradesh State Film Awards (Nandi Awards), six Tamil Nadu State Film Awards, Filmfare Lifetime Achievement Award and an Orissa State Film Award, in addition to SIIMA Lifetime Achievement Award. In 2009, she was honored with the Doctorate from the University of Mysore. She has been awarded the Kalaimamani Award from the Government of Tamil Nadu and Karnataka Rajyotsava Award from the Government of Karnataka. In 2013, she was honored by the Government of India with the Padma Bhushan, the third-highest civilian honour of the country. However, she refused to accept it expressing dissatisfaction over the number of people from South India figuring in the Padma Awards list for that year.

Janaki's contribution to the Indian music industry in a career spanning six decades gained her honorific titles such as the "Queen of Melody", "Nightingale of South India", and "Expression Queen". She has recorded over 48,000 songs in films, albums, TV and Radio which includes solos, duets, chorus and title tracks in over 17 languages including Kannada, Malayalam, Telugu, Tamil, Hindi, Sanskrit, Odia, Tulu, Urdu, Punjabi, Badaga, Bengali, Konkani and also in foreign languages such as English, Japanese, German and Sinhala; the highest number of songs in her career were in Kannada followed by Malayalam. She began her singing career with the Tamil film Vidhiyin Vilayattu (1957) and recorded in six languages in the same year. Her career has spanned over six decades until 2016, when she announced self-retirement from singing for films and stage appearances. However, upon insistence from the film fraternity, she made a comeback by singing a song for the Tamil film Pannaadi in 2018.

Widely acclaimed as one of the most versatile singers, her association with singer S. P. Balasubrahmanyam and composer Ilaiyaraaja is most talked about. In the 1960s, 1970s and 1980s her duets with P. B. Srinivas, S. P. Balasubrahmanyam, K. J. Yesudas, P. Jayachandran and Dr. Rajkumar topped the charts across all the South Indian languages. She has sung in almost all the genres and has performed live on stage in more than 5000 concerts across the globe.