Episodes generally consist of two four-person teams in competition, plus one or two hosts who usually consult with an "expert" judge who knows something about non-junk versions of the machines being constructed. Each team consists of three regular members, plus a fourth expert who usually has a better understanding of the class of machine being constructed for that episode.
The challenges are many and varied, but usually involve teams constructing a machine to achieve a particular objective. Challenges usually involve understanding of a particular scientific priciple e.g. ballistics, navigation etc. The final showdown usually consists of either head to head races or individually run timed events.
The idea for the show came from a scene in the movie Apollo 13, where NASA engineers had only a short period of time to construct an air filter out of parts available on the space capsule.
Scrapheap Challenge originated on the British Channel 4, but was imported to United States television under the name Junkyard Wars. Later, an American version of the show was created with the same name.
In the United Kingdom, the two programs have distinct names, but American audiences only see the Junkyard Wars title. Sometimes, video of the UK version is even edited to blot out the name Scrapheap Challenge. The UK programme is presented by Robert Llewellyn and Lisa Rogers.
The first series of the show, in the UK, pitted the same two teams against each other each week, and was simply titled Scrapheap. The Challenge part was added when the gauntlet was thrown down to new competitors, and a knockout championship process was created.