In Mondo, players compete against each other while also racing against the clock. Each player has a small world board with empty spaces on it, and all players simultaneously pick tiles depicting different animals and environments from the middle of the table and place them on their world board, trying to create complete areas of the same environment. A new tile must be placed next to an already placed tile, but the environmental borders don't have to match. (These errors will earn negative points when the board is scored.)

When the timer runs out, players score bonus points for each animal and each completed environment and score negative points for volcanic tiles, empty fields on the world board and mismatched tiles (for example, a tile with a forest border connecting with a tile with a water border).

Mondo includes three degrees of difficulty, in addition to additional goals and ways to achieve (and lose) bonus points, as well as rules for solo play.