The couple, who had split in 2009, still have great chemistry, as this photograph shows.
Ek Tha Tiger will be a romantic thriller. It will be directed by Kabir Khan (Kabul Express, New York) and produced by Aditya Chopra.
This is the first time that Salman will be working in a Yash Raj film.
"I am honoured to work with Yash Chopra, who has had a long standing relation with my father. They have worked closely in the past," Salman said.
Is it a superhero film? "No, it's not," Salman quipped. "It is a hero's film."
The shooting will start in July.
Salman and Katrina were last seen together in Subhash Ghai's Yuvvraaj in 2008.