Legends of Runeterra (LoR) is a 2020 digital collectible card game developed and published by Riot Games. Inspired by the physical collectible card game Magic: The Gathering, the developers sought to create a game within the same genre that significantly lowered the barrier to entry. Since its release in April 2020, the game has been free-to-play, and is monetised through purchasable cosmetics. The game is available for Microsoft Windows and mobile operating systems iOS and Android.

Like other collectible card games, players play one versus one to reduce their opponent's health to zero. Cards come in a variety of types and belong to one of ten regions—groups of cards with a similar gameplay identity. One significant feature is the game's combat pacing; unlike in other collectible card games, each player alternates between attacking and defending every turn.

Many characters from League of Legends, a multiplayer online battle arena by Riot Games, feature in the game. The fictional universe of Runeterra, released by the developer through short stories, comic books, and an animated series, provides flavor and theming for the game's cards.

Legends of Runeterra has been well received by critics, who point to its generous progression systems, accessible gameplay, and high-quality visuals, and has won several industry awards.

Legends of Runeterra is a digital collectible card game played one versus one. At the beginning, both players' Nexus has 20 health points; the first to fall to zero loses. Players begin each match with a hand of four cards, which they may trade away for another random card from their deck. Each round, both players draw one card. Cards are played by spending mana; players begin with zero mana, and gain one additional mana crystal per round up to a maximum of ten. A maximum of three unspent mana is stored automatically at the end of a round as spell mana; this can be used in future rounds to cast spells but cannot summon unit cards.

One of the game's distinguishing features is its combat pacing. Each round, the "attack token", a symbol which indicates which player may attack and who will defend, alternates from player to player. This is reflected visually on each players' half of the board, with a sword icon representing attack or a shield for defense. Some cards enable players to attack when they do not have the attack token.

Each card in the game belongs to a region; in standard play, one deck can use cards from up to two regions. Regions have a distinct style of play and identity. Unlike other trading card games, there are no neutral cards that can be used in every deck. The regions originated in the wider League of Legends expanded universe. Upon the game's initial release, there were three types of card: champions, followers, and spells. Champion cards are the playable characters from League of Legends. These cards are unique within the game because they can level up. Levelling a champion transforms the card—and all copies of it in the player's deck—into a more powerful version of the card. Unit cards, which includes champions and non-champions (followers), have a number representing their attack and health statistic; attack is how much damage a unit deals to either the Nexus or its blocker, while health reflects the maximum damage a card can take before being removed from play.

Spell cards have a "speed", denoting when they can be played and in what way the opponent is able to respond, if at all. At launch, there were three speeds: slow, fast, and burst. Slow-speed spells cannot be played during active combat, pass priority over to the opponent, and can be responded to with fast or burst spells; fast spells can be played during combat and do not pass priority; and burst speed spells resolve their effect instantly with no opportunity for opponent response. A fourth speed, Focus, resolves immediately and does not pass over turn priority, but can only be used outside of combat. Unit cards do not have a speed, but end a player's turn within a round.