Anusandhan (in Bengali ; English: Discovery) or Barsaat Ki Ek Raat (in Hindi ; English: One Rainy Night) is a 1981 Indian bilingual action thriller film made in both Bengali and Hindi languages, produced and directed by Shakti Samanta under his banner of Shakti Films. Based on a novel named Anusandhan by Shaktipada Rajguru, it stars Amitabh Bachchan, Rakhee Gulzar, Amjad Khan, Utpal Dutt and Prema Narayan in lead roles, while Tarun Ghosh, Abhi Bhattacharya, Asit Sen, Sujit Kumar, Amarnath Mukherjee play other supporting roles, with Nimu Bhowmik in a special appearance. The Hindi version was an average grosser.

The film is remembered for the classic songs "Haye Wo Pardesi","Apne Pyar Ke Sapne Sach Hue" and "Kaliram Ka Khul Gaya Pol". The first song was remade by the Bombay Bicycle Club and the second was used in the international song Funky Bijou Anthem.