The Four Colour Theorem is an important theorem in mathematics which states that the minimum number of colours required to colour in a map so that no two areas with the same colour are adjacent is four. There are some restrictions on the types of maps that can be coloured.

The theorem was first stated as a conjecture (something which is believed to be true, but hasn't yet been proved) over 150 years ago. It was finally proved, using computers to check all the possible different configurations of maps, in 1976 by mathematicians John Koch, Kenneth Appel and Wolfgang Haken. The proof was quite controversial at the time, because this was the first time that computers had been used to help to prove a serious mathematical theorem.