Chess960, also known as Fischer Random Chess, after its inventor, World Chess Champion Bobby Fischer, provides a variety of chess opening positions, obviating reliance on opening theory. There are 959 possible positions, plus the classical one, hence the name.
Setting up the board
As in classical chess, the pieces begin on the first rank and the pawns on the second, and the positions of black and white are arranged to mirror each other, with queen opposite queen, and so on.
What is different is that the pieces are distributed randomly according to an agreed method, with provision made for the bishops to occupy different coloured squares and for the king to be between the rooks, so that castling is possible.