Tien Len can be considered the national card game of Vietnam; the name of the game, which should properly be spelled Tiến Lên, means Go Forward. The main description on this page is based on information from Jona Baily; Kenneth Lu and Justus Pang have contributed slightly different versions. Probably as a result of the Vietnam war, Tien Len has spread to some parts of the USA, where it is sometimes called Viet Cong or just VC; Kelly Aman has contributed one version of this. Chris Hovanic learned another version from Chris Molinaro (also in the USA) and they call it Thirteen.
Tien Len is a climbing game (a bit like Zheng Shangyou or President), in which the aim is to get rid of your cards as soon as possible by beating combinations of cards played by the other players.
The game is for four players. A standard 52 card deck is used; there are no Jokers and no wild cards. It is possible for two or three to play. It can also be played by more than four players, using two 52 card packs shuffled together.
The game is normally dealt and played clockwise, but can be played anticlockwise instead if the players agree in advance to do so.
The ranking of the cards is: Two (highest), Ace, King, Queen, Jack, Ten, Nine, Eight, Seven, Six, Five, Four, Three (lowest).
Within each rank there is also an order of suits: Hearts (highest), Diamonds, Clubs, Spades (lowest).
So the 3 of Spades is the lowest card in the pack, and the 2 of Hearts is the highest. Rank is more important than suit, so for example the 
8 beats the 
7.
For the first game, the dealer is chosen at random; subsequently the loser of each game has to deal the next. When there are four players, 13 cards are dealt to each player.
If there are fewer than four players, 13 cards are still dealt to each player, and there will be some cards left undealt - these are not used in the game. An alternative with three players is, by prior agreement, to deal 17 cards each. When there are only two players, only 13 cards each should be dealt - if all the cards were dealt the players would be able to work out each other's hands, which would spoil the game. When there are more than four players, you can agree in advance either to deal 13 cards each from the double deck, or deal as many cards as possible equally to the players.
In the first game only, the player with the 3 of Spades begins play. If no one has the 3 (in the three or two player game) whoever holds the lowest card begins. The player must begin by playing this lowest card, either on its own or as part of a combination.
In subsequent games, the winner of the previous game plays first, and can start with any combination.
Each player in turn must now either beat the previously played card or combination, by playing a card or combination that beats it, or pass and not play any cards. The played card(s) are placed in a heap face up in the centre of the table. The play goes around the table as many times as necessary until someone plays a card or combination that no one else beats. When this happens, all the played cards are set aside, and the person whose play was unbeaten starts again by playing any legal card or combination face up to the centre of the table.
If you pass you are locked out of the play until someone makes a play that no one beats. Only when the cards are set aside and a new card or combination is led are you entitled to play again.
Example (with three players): the player to your right plays a single three, you hold an ace but decide to pass, the player to your left plays a nine and the player to right plays a king. You cannot now beat the king with your ace, because you have already passed. If the third player passes too, and your right hand opponent now leads a queen, you can now play your ace if you want to.
The legal plays in the game are as follows:
3 and the highest is the 2.
7-
7 or Q-Q.
5-5-5 9-9-9-9.
4-5-6 or J-Q-K-A-2. Sequences cannot "turn the corner" between two and three - A-2-3 is not a valid sequence because 2 is high and 3 is low.
In general, a combination can only be beaten by a higher combination of the same type and same number of cards. So if a single card is led, only single cards can be played; if a pair is led only pairs can be played; a three card sequence can only be beaten by a higher three card sequence; and so on. You cannot for example beat a pair with a triple, or a four card sequence with a five card sequence.
To decide which of two combinations of the same type is higher you just look at the highest card in the combination. For example 7-7 beats 7-7 because the heart beats the diamond. In the same way 8-9-10 beats 8-9-10 because it is the highest cards (the tens) that are compared.
There are just four exceptions to the rule that a combination can only be beaten by a combination of the same type:
Note that these exceptions only apply to beating twos, not other cards. For example, if someone plays an ace you cannot beat it with your four of a kind, but if the ace has been beaten by a two, then your four of a kind can be used to beat the two.
As players run out of cards they drop out of the play. If the player whose turn it is to play has no cards left, the turn passes to the next player in rotation. The play ends when only one player has cards left. That player is the loser, and must pay a fixed stake to each of the other players.
This game is often played for money, and sometimes for high stakes. Among serious players, typically the loser of a game would have to pay $2000 to each of the others. In a session of play, a person might easily lose (or win) a total of $50000 or more.
Some types of behaviour which in many other card games would be regarded as cheating are generally considered acceptable in Tien Len. For example among some players it OK to peek at other players' cards, or to play out of turn if you can get away with it.
In the version contributed by Justus Pang:
3 may pass rather than playing that card. This could be advantageous if the 3 is part of a bomb.The version of Tien Len contributed by Kenneth Lu has the following differences:
3 (or the 3 if the 3 was the undealt card). If there are only two players they are just dealt 17 cards each.3 leads, the lead does not have to include the 3. The first player may lead anything.The rules of Viet Cong (VC) as reported by Kelly Aman have the following features:
3 must begin with a combination that includes that card. Vinagames offers a Java on line Tien Len game.
Dracis also offers an online Java Tien Len game.