8 Out of 10 Cats Does Countdown as part of its 30th anniversary celebrations. Amongst the programmes that were chosen to be merged for the evening of specials, production teams on "Countdown" and "8 Out of 10 Cats" agreed to merge the two formats of their respective programmes together - the crossover between the two formats meant that "Countdown"s arrangement of games would be interspersed with "8 Out of 10 Cats"-style banter. As part of the merger, both Rachel Riley and Susie Dent assumed their roles from the programme, while Jimmy Carr took on the mantle of host, with both Sean Lock and Jon Richardson competing as
8 Out of 10 Cats Does Countdown and Jon Richardson as permanent team captains (various other personalities, such as Lee Mack, Sarah Millican, Bill Bailey and Claudia Winkleman, deputise when either captain is unavailable to film). Rachel Riley and Susie Dent take up their regular roles from "Countdown"; Joe Wilkinson appears in many earlier episodes as Rachel's assistant and has also stood in as a team captain. The formation of the crossover began as a series of specials, the first of which was conceived on 2 January 2012, when Channel 4 orchestrated a special "mash-up night", merging two shows to form a special edition of the pair,