Legends of Runeterra is played 1v1. Each player begins the match with a hand of four playing cards randomly selected from their card deck, a 20-health-point nexus, and zero mana. Before the match begins, each player also has the option to trade out any of the first four cards they drew for random different ones from their deck.
After this pre-game phase concludes, both players receive a mana gem, one player receives the attack token, and the other receives the defense token. Only the player with the attack token may attack during this round. After each round, the tokens switch between players, and each player draws a random card from their deck. As the number of rounds increases, so too does the number of mana gems each player receives, up to a maximum of 10. At the end of each round, any unused mana becomes spell mana, up to a maximum of three. This mana can only be used to cast spell cards.
To play cards, players must spend mana gems. There are three types of cards: Champions, Followers, and spells. Champions are the most powerful cards in the game, and each has a criterion that, once met, will level up the card to a more powerful version. Followers consist of all other normal playable cards and spells cause effects when played.
Once played, cards may be placed forward once more to either attack or defend with. When attacking, if no opposing card blocks, the card will hit the enemy player's nexus, dealing damage equal to its power stat. If the attacking card is defended against a blocking card, the two cards will clash, dealing their respective damage amounts to one another. Each card also has a defense stat. If the damage received is greater than or equal to the defense stat of the card, it is destroyed. Striking an enemy nexus with a card deals no damage to the attacking card. The objective of the game is to bring the opponent's nexus to zero health points.