This article was originally based on Western sources, but then was corrected by Anthony Kam (antkam@mit.edu).
Some of the rules given here might be regional variations, since Mr. Kam is from Hong Kong.

"Tien Gow" means "Sky Nine" and takes its name from "Sky" or "Heaven" being the top civilian piece and nine being the top military piece.

Players and Equipment
Tien Gow is a four player game using one set of Chinese dominoes. The goal of the game is to win points by taking tricks,
much like a Western card game.

It is a (zero-sum) gambling game. The players start with some money and money changes hand according to the scoring rules.
The game is not played in points in the sense of Bridges or Hearts, but more like points in the sense of Rubber
Bridge where points are trades for money (for example, $1 per 10 points).

The Deal and Bidding
Throw dice to choose a banker for the first hand. The banker puts a small puck or other marker on the table in front of him.
Mah Jong uses a device showing the points of the compass and it could certainly be used in Tien Gow, but any marker will do.

The banker stacks up a woodpile and deals each player a hand of eight tiles. The banker also leads the first trick of the hand.
The winner of each trick leads the following trick. The winner of the last trick in a game becomes the first banker in the next game.

A player leads a set of tiles as follows:

one tile (singleton)
a pair of tiles (bo or pair)
a set of 3 tiles (triplet)
a set of 4 tiles (quartet)
Each player in turn then plays a set composed of the same number of tiles.
When all players have played, this constitutes one trick. A player may play any tiles but if that set does not beat the current high
set then they must be played face down as discards. This introduces a guessing element into the game, as you cannot
count the tiles perfectly. If a player's set is better than the current high set those tiles may be played face up and become the new high set.
After all four players have played, the player who played the high set takes the trick.

Rank and Suit of the Tiles
Tiles in a set of Chinese dominoes are divided into two suits (civilian and military). See below for the classification and ranking (top to bottom).