Gleaned from http://www.unorules.com, http://www.wonkavator.com/uno/unorules.html, https://en.wikipedia.org/wiki/Uno_(card_game) and then heavily edited.
The aim of the game is to be the first player to score 500 points. This is achieved (usually over several rounds of play) by a player discarding all of their cards and earning points corresponding to the value of the remaining cards still held by the other players.
The deck consists of 108 cards, of which there are twenty-five of each color (red, green, blue, and yellow), each color having two of each rank except zero. The ranks in each color are zero to nine, "Skip", "Draw Two" and "Reverse" (the last three of these being classified as "action cards"). In addition, the deck contains four each of "Wild" and "Wild Draw Four" cards.
To start a hand, seven cards are dealt out to each player, and the top card of the deck is flipped over and set aside to begin the discard pile. The player to the dealer's left plays first, unless the first card on the discard pile is an action or Wild card (see below). On a player's turn, he/she must do one of the following:
- play a card matching the discard in color, number or symbol
- play a Wild card, or a playable Wild Draw Four card (see restriction below)
- draw the top card of the deck
If a player chooses to draw the top card of the deck, and that card is playable (it matches the discard, or is a playable wild card), then the player may (but need not) immediately play that card.
Play proceeds clockwise around the table.
Action and Wild cards have the following effects:
| Card | Effect when played from hand | Effect as first discard |
|---|---|---|
| Skip | Next player in sequence misses a turn | Player to dealer's left misses a turn| |
| Draw Two | Next player in sequence draws two cards and misses a turn | Player to dealer's left draws two cards and misses a turn |
| Reverse | Order of play switches directions (clockwise to counterclockwise, and vice versa) | Dealer plays first; play proceeds counterclockwise |
| Wild | Player declares next color to be matched (may be used on any turn even if the player has matching color) | Player to dealer's left declares first color to be matched, then plays normally |
| Wild Draw Four | Player declares next color to be matched; next player in sequence draws four cards and loses a turn. May be legally played only if the player has no cards of the current color; Wild cards and cards with the same number or symbol in a different color do not count | Return card to deck, shuffle, flip top card to start discard pile |
- A player may draw a card from the deck even if that player has a playable card.
- If a player chooses to draw a card and the drawn card is playable, the player has the option of either keeping it or playing it immediately (as part of that turn).
- If a player does not have a playable card, the player will continue to draw until a playable card is drawn. If deck is empty during draw, flip over used cards and continue.
- A player may play a Wild card at any time (even if that player has other playable cards).
- A player may play a Wild Draw Four card only if that player has no cards matching the current color (the player may have cards of a different color matching the current number or symbol or a Wild card). A player who plays a Wild Draw Four may be challenged by the next player in sequence (see below).
- If the entire deck is used during play, the top discard is set aside and the rest of the pile is shuffled to create a new deck. Play then proceeds normally.
- It is illegal to trade cards of any sort with another player.
- In a two-player game, the Reverse card acts like a Skip card, thus the other player misses a turn.
A player who plays his/her next-to-last card must call "uno" as a warning to the others.
The first player to get rid of his/her last card ("going out") wins the hand and scores points for the cards held by the other players. Number cards count their face value, all action cards count 20, and Wild and Wild Draw Four cards count 50. If a Draw Two or Wild Draw Four card is played to go out, the next player in sequence must draw the appropriate number of cards before the score is tallied.
When the first player reaches 500 points, that person wins the game.
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If a player lays down his/her second-to-last card without calling "UNO" and is caught before the next player in sequence takes a turn (draws a card from their hand, draws a card or touches the discard pile, depending on interpretation), he/she must draw two cards. One must lay the card before calling uno. If the player is not caught in time, or remembers to call "uno" before being caught, he/she suffers no penalty. If a player calls out uno wrongly he/she must draw two cards.
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When a Wild Draw Four card is played, the next player in sequence has the right to challenge it if he/she believes the player has at least one card in the current color. The player who played that card privately shows his/her cards to the next player. If the challenge is successful, the player who played the Wild Draw Four must draw four cards and the next player goes, otherwise the next player must draw six cards and miss a turn. Regardless of the outcome, the Wild Draw Four remains on the discard pile, and the color named by the player who used it remains in effect.
A strategy at Uno may be offensive (aiming to go out), or defensive (aiming to minimize the score of the hand, in the event that another player goes out). Part of the skill of playing Uno is knowing when to adopt an offensive or defensive strategy.
An offensive strategy would advise holding on to Wild and Wild Draw Four cards, because these can be played near the end of the hand in order to go out (when it may be hard or impossible to play a matching card). However, a defensive strategy would advise getting rid of such cards early, because they have a high point value.
A defensive strategy would advise playing a high-numbered card in order to reduce the point value of the hand. However, an offensive strategy would suggest playing a 0 when the player wants to continue on the current color, because it is less likely to be matched by another 0 of a different color (there is only one 0 of each color, but two of each 1–9).
A player holding only one card is required to call out "uno" or risk being penalized if caught. A player who calls "uno" risks being the target of concerted action from the other players, who may be able to use action cards to prevent that player from having an opportunity to go out. Depending on the level and seriousness of play, some players may deliberately avoid saying "uno", in the hope of avoiding detection and then going out on the next turn. For this reason, it is useful to conceal how many cards are in your hand, and to keep track of how many cards every other player holds.
Little has been published on the optimal strategy for the game of Uno. Simulations of games may shed some light on the matter, but the game solution is likely to be very complex. This is because attempts to reduce point count in the player's hands can be "read" by other players if too transparent. This information can be exploited by other players, and it follows that a mixed strategy may be more appropriate.
The new Uno action cards bear symbols which denote their action, except for the Wild cards which still bear the word "Wild." Before the design change, such cards in English versions of the game bear letters. Especially old English versions can be denoted by the absence of the white rim that surrounds the edge of most Uno cards. Other versions also use symbols and images in both old and new designs, especially those with Wild cards that do not bear the word "Wild" in 40th Anniversary sets. The Xbox 360 version of the game uses the new English style of the cards in gameplay. There are also language-free versions of the newer styles Uno action cards that do not bear the word "Wild" but have the same styling.