British Square is a solitaire card game which uses two decks of 52 playing cards each. It has an unusual feature of switchback building whereby each foundation is first built up (from ace to king) and then built down (from king to ace).

First sixteen cards are dealt on the tableau into four columns of four cards each, turning it into a "square." American rule sets, though, puts the formation of the tableau at sixteen piles, four rows of four piles each. Each pile contains a card at the start of the game.

The object of the game is to free an ace of each suit to make four foundations, then to build them up by suit up to Kings, placing the second King of each suit and finally to build them down, again by suit, to Aces.

The top cards of each column is available for play, to be placed either on the foundations or on other columns in the tableau. In the cast of American rules sets, the top card of each pile is available.

When building on the tableau, they can be built either up or down by suit. But once a card has been built, it indicates the direction of building on the column; it cannot go both ways. For instance, when the 8♥ is placed on the 7♥, the next card to be built should be the 9♥. If the reverse happens (7♥ over 8♥), the next card should be 6♥. The direction can be altered by having the top card of the sequence placed on an appropriate card and have all other cards on the sequence follow. Furthermore, building is not round-the-corner; i.e. a sequence can be built only up to Kings/down to aces.

Cards can be moved one a time. Any empty column is filled with a card from either from the stock or from the wastepile.

When moving cards on the tableau is no longer possible, the stock is dealt one card at a time and any applicable card is placed on the foundations or on the tableau. The stock can only be dealt once.

The game is won when all cards are built to the foundations. There are four foundations, one for each suit. As mentioned above, they should be built first up by suit to kings, then the second king is placed on the first and built down to aces.