Alternation is a solitaire card game which is played using two decks of playing cards. Its tableau (or playing area) is similar to that of another solitaire game Stonewall.
Forty-nine cards are set up into seven columns of seven cards each. Keep in mind that in each column, the top card, as well as the third, fifth cards from the top and the bottom card, are face up, while the second, fourth, and sixth cards from the top are face down, much like the pattern OXOXOXO.
The object of the game is to release the Aces as they become available and built each of them by suit.
The top cards of each column are the only ones available for play, to be built up by suit on the foundations, or on each other down by alternating colors. A sequence or part of a sequence can be moved as a unit.
When no more cards can be moved, the stock (the remaining cards) is dealt one card at a time. A card that cannot be built on the tableau or on the foundations is placed on the waste pile, the top card of which is available for play.
The game ends soon after the entire stock has run out. The game is won when all cards are built onto the foundations.
(Retrieved from http://en.wikipedia.org/wiki/Alternation)