Game Overview:
UNO is a fast paced card game for two to ten players  ages seven  and up. The idea of the game is to get to your last card, shout “UNO!” before another player realizes you didn’t, and then attempt to play your last card on your turn to win the round. The player to use up his or her last card wins the round and is scored based on the cards left in their opponent’s hand.

Setup:
The game starts by having every player draw a single card. Highest value card wins dealer (yay?), but all action cards are valued at 0 for this phase of the game. The cards are reshuffled back into the deck and each player is dealt seven cards, with the remaining cards placed face down to form a draw pile. Take the top card from the draw pile and place it face up to begin a discard pile.

Gameplay:
The player on the left of the dealer starts the round by matching a card in his hand  by color or number  with the top card on the discard pile.  If he cannot, then he must draw a card.  He can play the newly drawn card if able,  but the turn ends whether he plays the card or not.
Matching is defined as placing a card of the same color or number on top of the top card of the discard pile. For example,  a blue two may be placed upon a yellow two. Likewise a yellow draw two and a blue draw two may be played on top of each other. A green three placed upon a green five is also a legal play. The only cards that are not required to match to be played are Wild and Wild Draw 4 cards.
A player may choose not to play a card and to draw a card instead. They may play the card they drew, but may not play a card from their hand after drawing a card in this way. Play continues until one player runs out of cards thus ending the round. If the draw pile ever runs out of cards then the discard pile, minus the top card, is shuffled and turned back over to replenish the draw pile.

Contents:
There are 108 cards in total, 4 colors and 19 cards in each color (0 to 9), 24 action cards, and 8 wild cards.
Action Cards:

Draw two:
This card forces the next player to draw 2 cards. If you are playing heads up (two players) then this card also skips your opponent. If turned up as the first card in play, then the first person to play also draws 2 cards. If playing heads up, this card also skips your opponent in addition to its normal effect.

Reverse:
This will reverse the direction of play originating from the person who played the card. If play was moving right, then now it is moving left. If this card is placed face up at the beginning of play, then the play is reversed and the dealer goes first. If playing heads up then this card simply skips your opponent.

Skip:
Skips the next player to play. If placed face up at the beginning of play, this card skips the first player to the left of the dealer.

Wild Card:
This card can be played on any color at any time. Once played, the person who played the card calls a color. The discard pile is now that color and play continues. If this card is the first card played then the person to the left of the dealer calls the color.
Wild Draw 4:
This card may only be played legally if you have no other card that matches the COLOR of the discard pile. If you choose to play this card while not meeting that specific requirement, then your opponents have the option to call you on it. Please see special rules below for penalties. Once the card is laid down, a color is called by the issuer, and the next person to play draws 4 cards. If this card is turned up at the beginning of play, it is shuffled into the deck and another card is drawn to replace it. Wild Draw 4’s cannot start the game.
Penalty Box:
There are specific penalties that players need to know about that are not listed on the cards.

1. Players must call out “UNO!” when their second to last card is played. Failure to do so can result in 2 additional cards being drawn if your opponents realize your omission.  You may say it at any time after this point, but if your opponents catch you before you do then you are penalized just the same.
2. You may not make a card suggestion to another player. The offending player must draw 2 cards.
3. If a player intentionally or accidentally plays the wrong card, and allows another player to catch his error, then that person is required to take the wrongfully played card back, and draw an additional 2 cards.
4. Wild Draw 4 can only be played legally if the person playing the card has no matching colors for the discard pile. If this card is played, and foul play is suspected, the player expected to pick up the 4 cards, and only this player, may challenge the play. Once challenged the person who originally played the card must now show their hand to the challenger. If the card is found to be played illegally, then the person who played the draw 4 must now draw 4 cards instead of the challenger. If the challenger is wrong, then she must draw 4 cards and an additional 2 penalty cards.
Winning the game:
To win the game you must obtain a score of 500 points. You get point’s dependant on the remaining cards in your opponents hand when you go out. If a player “goes out” on a draw 2 card or draw 4 card, then the next player must still draw those cards and those cards are added to the tally.
Point Values:
0-9 are face value
Draw 2, Skip, and Reverse are 20 points
Wild and Wild Draw 4 are worth 50 points
Start the game over as a new round until one player reaches the winning point tally and is declared the winner.

Special Rules or Modes:
Elimination mode:
When a player “goes out” then each player tallies the card left in their own hands and adds those points to their total. Players are eliminated by reaching a predetermined number, such as 500 for example.  Play continues until all but two players are eliminated, and then switches to heads-up.
Group Play:
Players may play in teams, and if doing so all players draw appropriate hands. However, play alternates between teams and players inside those teams.  If player A and B are against C and D, and Team AB were first,  then the play would go: A plays, then C, then B, then D. First team to have a single player go out wins and the remaining cards in their opponents hand are tallied. Teams may talk amongst themselves, but may not trade or give away cards to each other.