Underbelly is an Australian television true crime-drama series which broadcasts on the Nine Network. Each series is based on real-life events.

The first series is based on the book Leadbelly: Inside Australia's Underworld, by The Age journalists John Silvester and Andrew Rule. The series also borrows the title 'Underbelly' from a previously successful series of 12 True Crime novels by the same authors, three direct tie-in novels were also later published as part of this series, and a separate 16th book (Underbelly: The Golden Casket) was published in 2010. The fourth series is based on the book Razor by crime author Larry Writer.

The fifth series titled Underbelly: Badness is based on Sydney underworld figure Anthony "Rooster" Perish, his brother Andrew and their associates, and is set between 2001–2012, broadcast from 13 August 2012. A sixth series titled Underbelly: Squizzy, based on the events surrounding Joseph "Squizzy" Taylor set between 1915–1927, began airing on 28 July 2013.

Three telemovies called The Underbelly Files aired in 2011. The movies were titledTell Them Lucifer was Here, which is about the 1998 murders of Victorian police officers Gary Silk and Rod Miller and the subsequent manhunt for their killers, Infiltration, is about the story of Australian police detective Colin McLaren's infiltration of the Calabrian Mafia in Griffith, New South Wales which saw dozens of underworld figures imprisoned, and The Man Who Got Away,which tells the story of David McMillian, a drug smuggler and the only Western man to ever escape from Bangkok's Klong Prem Central Prison. All three aired on the Nine Network in February 2011.

In September 2011, a New Zealand version of the series premiered on TV3, titled Underbelly NZ: Land of the Long Green Cloud the six part mini-series was the first Underbelly production to be produced and financed outside of Australia. The series detailed events beginning in the late 1960s to and throughout the 1970s and told the origin of the Mr Asia drug syndicate and its original leader Marty Johnstone. The series is somewhat a prequel to the series A Tale of Two Cities. An American version has also been announced on the network channel Starz though nothing else has been confirmed at this stage.