Mad as a Hatter is the debut EP by Australian hip hop group Def Wish Cast. It was released in 1992 on vinyl by Random Records. All production and turntablism is by DJ Vame, except "Proppa Ragga", which was produced by DJ Sing. "Proppa Ragga" was the first Australian hip hop track to receive international recognition, albeit at Norway, coming in at number 2 on its NRK's Hip Hop show (hosted by Tommy Tee). In 2007, a copy of Mad as a Hatter sold on eBay to a German bidder for more than A$430. The EP samples Walt Disney's Alice in Wonderland in the title track.

"Mad as a hatter" is a colloquial phrase used in conversation to refer to a crazy person. In 18th and 19th century England, mercury was used in the production of felt, which was used in the manufacturing of hats common of the time. People who patronised these hat factories were exposed daily to trace amounts of the metal, which accumulated within their bodies over time, causing some workers to develop dementia caused by mercury poisoning (called mad hatter syndrome). Thus, the phrase became popular as a way to refer to someone who was perceived as insane.