Cluedo is a mystery crime fiction board game originally published by Waddingtons in 1949. It was devised by Anthony E. Pratt, a solicitor's clerk and part-time clown from Birmingham, England.

It is now published by the United States game and toy company Hasbro, which acquired its U.S. publisher Parker Brothers as well as Waddingtons.

The game is set in a mansion, with the board divided into different rooms. The players each represent a character who is a guest staying at this house, whose owner, Dr. Black (Mr. Boddy in the North American version), has been found murdered.

Players attempt to solve the murder. The solution to the murder requires the three components of Suspect, Weapon, and Room.

More games, books, and a film have been released as part of the Cluedo franchise. The board games form an overall story whose complete chronology can be found at Cluedo chronology.

At the beginning of play, three cards, one Suspect, one Weapon, and one Room card are chosen at random and put into a special envelope, so that no one can see them. These cards represent the true facts of the case. The remainder of the cards are distributed among the players.

The aim is to deduce the details of the murder; that is, the cards in the envelope. There are six different characters, six possible murder weapons and nine different rooms (typically Hall, Lounge, Dining Room, Kitchen, Ballroom, Conservatory, Billiard Room, Library, and Study), giving 324 possible solutions.

In the course of determining the details of the murder, players announce suggestions to the other players, for example, "I suggest it was Mrs. White, in the Library, with the Rope." All elements contained in the suggestion are moved into the room in the suggestion.

The other players must then disprove the suggestion, if they can. This is done in clockwise order around the board. A suggestion is disproved by showing a card containing one of the suggestion components to the player making the suggestion (for example, the Rope), as this proves that the card cannot be in the envelope.

Showing the card to the suggesting player is done in secret so the other players may not see which card is being used to disprove the suggestion. Once a suggestion has been disproved, the player's turn ends and moves onto the next player.

The player's suggestion only gets disproved once. So, though several players may hold cards disproving the suggestion, only the first one will show the suggesting player his or her card. A player may only make a suggestion when his or her piece is in a room and the suggestion can only be for that room.

Once a player has sufficiently narrowed the solution, that player can make an accusation. According to the rules, "When you think you have worked out which three cards are in the envelope, you may, on your turn, make an Accusation and name any three elements you want." You may name any room (unlike a Suggestion, where your character pawn must be in the room you suggest).

The accusing player checks the validity of the accusation by checking the cards, keeping them concealed from other players. If he has made an incorrect accusation, he plays no further part in the game except to reveal cards secretly to one of the remaining players when required to do so in order to disprove suggestions.

Also, according to the rules, "If, after making a false Accusation, your character pawn is blocking a door, you must move it into that Room so that other players may enter." Since a character pawn can only block a door by being outside of a Room, this clearly demonstrates that the character pawn need not be in any Room to make an Accusation. If the player made a correct accusation, the solution cards are shown to the other players and the game ends.

It is possible for a player to be using the piece representing the murderer. This doesn't affect the game play; the object of the game is still to be the first to make the correct accusation. If the game is played with two people, the process of elimination diffuses the same information to both players. Such a game tends to pass quickly. The Hasbro version of the game is not advertised as a two-player game.