Gangaajal: The Holy Weapon (transl. Holy Water) is a 2003 Indian Hindi-language action crime drama film written, directed, co-produced and edited by Prakash Jha. Featuring an ensemble cast of 87 actors, it revolves around the Superintendent of Police Amit Kumar (Ajay Devgn) who takes charge of the fictitious district of Tejpur, Bihar, known for its high crime rate and organised crime carried out by dons Sadhu (Mohan Joshi) and Sunder Yadav (Yashpal Sharma). Due to the local police's slow response to crimes, residents of the district resort to pouring acid in the eyes of the criminals as an instrument for extrajudicial justice.

Following the release of his directorial debut Damul (1984), Jha conceived an idea for his next venture that would be titled Gangaajal, which would be about corruption and political violence. Jha was unfamiliar with the subject matter and had no desire to start production, and took twenty years to write the story. The film, announced in January 2001, was photographed by Arvind K; filming took 60 days and took place in Wai and Satara, both in Maharashtra, and sets were designed by Sukhwant Panigrahi. The film's soundtrack was composed by Sandesh Shandilya with lyrics by Akhilesh Sharma and a background score by the American composer Wayne Sharpe.

Gangaajal was released on 29 August 2003. Its production costs were ₹45 million (US$560,000) or ₹100 million (US$1.3 million); the film was a moderate success at the box office, became one of the highest-grossing Indian films of the year, and grossed ₹166.7 million (US$2.1 million) worldwide. It received widespread acclaim from critics, some of whom praised the cast's performances—generally that of Devgn—but questioned the plot's originality. Gangaajal received several accolades, including the National Film Award for Best Film on Other Social Issues. A sequel titled Jai Gangaajal was released in 2016 which under-performed, both commercially and critically.