The dominos are turned face down, mixed up, and moved to a stock pile placed on one side of the table. Each player draws ten dominos, which he turns up for himself to see but keeps hidden from the other players.

The game consists of two phases. A preliminary phase involves laying down the foundation of a skyscraper; the second phase is the heart of the game and involves building the skyscraper up from the foundation.

Each player takes a turn placing any domino from his hand to a 4x4 playing area, then drawing a domino from the stock pile to replace it in his hand. It does not matter which dominos are played to the foundation, only that they are positioned and oriented in two columns of horizontal dominos, as in the following example:

Once the foundation is laid, players continue to take turns playing dominos, but at this point they can only play a domino on top of other dominos. A domino is legal to play somewhere upon the skyscraper if:

• The numbers on the domino being played match the numbers on the domino(s) it is to be placed upon.
• The domino is placed upon two numbers at the same height.

For example, let's say this is the first turn after the foundation is built, and the foundation looks like the diagram above. If the player whose turn is next has a 5-5 domino, he can place it in the lower right corner of the foundation, on top of the two fives adjacent to each other there.

He draws a replacement domino, and then it is the next player's turn. If the next player has the second 5-2 domino in his hand, he cannot play it over the two and five in the lower right, because now the two and five are at different heights, thanks to the previous player's 5-5 domino. He might, however, play a 4-2 domino right next to the 5-5. Then, if that area is untouched before his next turn, he'll be able to play the 5-2 domino on top of both the 4-2 and the 5-5.

Blanks are wild. The blank portion of a domino can go on top of any other number, and any part of a domino can be placed on top of a blank. In the example above, any domino with a five in it -- a 5-1, 5-5, 5-blank, or whatever -- can be placed over the lower left 5-blank.

If a player cannot play on his turn, he's out. The last player still in the game wins. Once the stock pile is exhausted, players continue to play but do not replenish their hands after each turn.

Note that it is possible to cut off certain squares in such a way that it's impossible to play on them ever again. In the example above, if a 6-5 domino is played on the right edge and a 3-2 domino is played on the top edge, the six in the upper right is cut off and can't be played on again, because it can't ever be built up to the height of the squares adjacent to it.

The nature of the gameplay changes subtly if you alter the number of dominos you start with in your hand. With ten dominos per hand, most games proceed beyond the point the stock pile is exhausted. With just eight dominos per hand, blind luck becomes more of a factor, but, paradoxically, so does strategy.