From the publisher's website:

Five dice are used per player with dice cups used for concealment. Each round, each player rolls a "hand" of dice under their cup and looks at their hand while keeping it concealed from the other players. The first player begins bidding, announcing any face value and the number of dice that the player believes are showing that value, under all of the cups in the game. Ones are often wild, always counting as the face of the current bid. Each player has two choices during their turn: to make a higher bid, or challenge the previous bid - typically with a call of "liar." Raising the bid means either increasing the quantity, or the face value, or both, according to the specific bidding rules used. There are many variants of allowed and disallowed bids; common bidding variants, given a previous bid of an arbitrary quantity and face value, include: - the player may bid a higher quantity of any face, or the same quantity of a higher face (allowing a player to "re-assert" a face value they believe prevalent if another player increased the face value on their bid); - the player may bid a higher quantity of the same face, or any quantity of a higher face (allowing a player to "reset" the quantity); - the player may bid a higher quantity of the same face or the same quantity of a higher face (the most restrictive; a reduction in either face value or quantity is never allowed). If the current player challenges the previous bid, all dice are revealed. If the bid is valid (at least as many of the face value and any wild aces are showing as were bid), the bidder wins. Otherwise, the challenger wins.