When the Levees Broke: A Requiem in Four Acts is a 2006 documentary film directed by Spike Lee about the devastation of New Orleans, Louisiana following the failure of the levees during Hurricane Katrina. It was filmed in late August and early September 2005, and premiered at the New Orleans Arena on August 16, 2006 and was first aired on HBO the following week. The television premiere aired in two parts on August 21 and 22, 2006 on HBO. It has been described by Sheila Nevins, chief of HBO's documentary unit, as "one of the most important films HBO has ever made." The title is a reference to the blues tune "When the Levee Breaks" by Kansas Joe McCoy and Memphis Minnie about the Great Mississippi Flood of 1927.

The documentary was screened at the 63rd Venice International Film Festival on August 31 and September 1, 2006. It won the Orizzonti Documentary Prize and one of two FIPRESCI awards. It was also shown at the 2006 Toronto International Film Festival on September 15 and September 16, 2006. It won three awards at the 59th Primetime Emmy Awards and received a Peabody Award.

The documentary is based on news video footage and still photos of Katrina and its aftermath, interspersed with interviews. Interviewees include politicians, journalists, historians, engineers, and many residents of various parts of New Orleans and the surrounding areas, who give first hand accounts of their experiences with the levee failures and the aftermath.

In the style of Michael Apted's Up series (a documentary series that interviews Apted's subjects every seven years), Lee planned to interview his featured subjects in Levees at least once more. In August 2010, HBO aired Lee's documentary series, If God Is Willing and Da Creek Don't Rise, which chronicles how New Orleans and the Gulf Coast area have fared in the five years following Hurricane Katrina.