Kahaani (IPA: [kəˈɦaːni]; transl. Story) is a 2012 Indian Hindi-language mystery thriller film co-written, co-produced, and directed by Sujoy Ghosh. It stars Vidya Balan as Vidya Bagchi, a pregnant woman looking for her missing husband in Kolkata during the festival of Durga Puja, assisted by Assist Sub-Inspector Satyoki "Rana" Sinha (Parambrata Chatterjee) and Inspector General A. Khan (Nawazuddin Siddiqui).

Made on a budget of ₹80 million (US$950,000), Kahaani was conceived and developed by Ghosh, who co-wrote the film with Advaita Kala. The crew often employed guerrilla-filmmaking techniques on Kolkata's streets to avoid attracting attention. Its creative portrayal of the city and its use of local crew and cast made it a notable film. Kahaani explores themes of feminism and motherhood in a male-dominated Indian society. The film also makes several allusions to Satyajit Ray's films, such as Charulata (1964), Aranyer Din Ratri (1970), and Joi Baba Felunath (1979). The film's musical score and soundtrack were composed by Clinton Cerejo and Vishal–Shekhar respectively, with cinematography handled by Setu and editing done by Namrata Rao.

Kahaani was released worldwide on 9 March 2012. Critics praised the screenplay, the cinematography and the performances of the lead actors. Following critical acclaim and word-of-mouth publicity, the film earned ₹1.04 billion (US$12 million) worldwide in 50 days. The film won several awards, including three National Film Awards and five Filmfare Awards. The latter included trophies for Best Director (Ghosh) and Best Actress (Vidya). The film was remade by Sekhar Kammula in Telugu as Anaamika (2014) with Nayanthara reprising Vidya's role. A spiritual successor, titled Kahaani 2: Durga Rani Singh, was released on 2 December 2016.

A poison gas attack on a Kolkata Metro Rail compartment kills all the passengers on board. Two years later, Vidya Bagchi (Vidya Balan), a pregnant British-Indian software engineer, arrives in Kolkata from London during the Durga Puja festivities in search of her missing husband, Arnab Bagchi. A police officer, Satyoki "Rana" Sinha, offers to help. Although Vidya claims that Arnab went to Kolkata on an assignment for the National Data Center (NDC), initial investigations suggest that no such person was employed by the NDC.

Agnes D'Mello, the NDC's head of human resources, suggests to Vidya that her husband resembled former employee Milan Damji, whose file is probably kept in the old NDC office. Before Agnes can provide any further help, she is killed by Bob Biswas, an assassin working undercover as a life insurance agent, at the entrance of her house. Vidya and Rana break into the old NDC office and find Damji's file, barely escaping an encounter with Bob, who is sent to search for the same information. Meanwhile, the attempts to obtain Damji's records have attracted the attention of two Intelligence Bureau officials in Delhi—the chief Bhaskaran K. and his deputy Khan. Khan arrives in Kolkata and reveals that Damji was a rogue IB agent responsible for the poison gas attack. Despite Khan's warnings, Vidya continues her search, fearing that Arnab's resemblance to Damji may have led him into trouble.

The address on Damji's record leads Vidya and Rana to a dilapidated flat. An errand boy from the neighbourhood tea stall identifies R. Sridhar, an NDC officer, as a frequent visitor to Damji's flat. Bob attempts, but fails, to kill Vidya and is soon run over by a truck during a chase. Examination of Bob's mobile phone leads Vidya and Rana to an IP address, sending instructions to kill her. They break into Sridhar's office to verify his IP address, but he is alerted electronically and returns to his office. Vidya accidentally kills Sridhar during a scuffle, which upsets Khan, who had wanted him alive.

Sridhar's computer data reveals a code, which when deciphered reveals Bhaskaran's phone number. Vidya calls Bhaskaran to tell him that she has retrieved sensitive documents from Sridhar's office. She asks Bhaskaran to help find her husband in exchange for the documents, but Bhaskaran tells her to contact the local police. Vidya soon gets a call from an unknown number, warning her that she should hand over the documents to the caller if she wishes to see her husband alive. Khan thinks the caller is Damji.

Vidya goes to meet Damji at the designated location as told in the phone call, followed by Rana and Khan. Damji cuts the meeting short when Vidya expresses her doubt that he will be able to return her husband in exchange for the sensitive file, and he attempts to leave. Vidya tries to stop him, and in the ensuing struggle, Damji draws a gun on her. Vidya disarms him using the prosthetic belly she has been using to fake her pregnancy and promptly stabbing him in the neck with her hairstick before finally killing him with his own gun. She flees into the crowd before the police arrive, leaving a thank-you note for Rana and a pen drive containing data from Sridhar's computer, which leads to Bhaskaran's arrest. Rana concludes that neither Vidya nor Arnab Bagchi ever existed and that Vidya had been using the police and the IB to achieve her own ends.