Here's Brad Pitt sharing a joke with Bill Clinton at the Clinton Global Initiative held in New York City on Thurdsay.

But it wasn't all light-hearted banter - the actor was at the annual event to talk about the progess of his Make It Right foundation, the project he established in 2007 to bring energy efficient housing to New Orleans in the wake of Hurricane Katrina.

He said: "I don't know how we build any other way anywhere else.

"We can no longer tell ourselves that implementing this technology is too complex a problem because it's just been proven on this little spot on the map."

The Clinton Global Initiative was established by the former US President to discuss solutions to climate change, poverty, global health and education issues.

Other famous faces at the event included Bono, Ricky Martin, Usher, Mira Sorvino, Julia Ormond and Jessica Alba.

See Brad's visit to the White House earlier this year