Hearthstone is a 2014 online digital collectible card video game produced by Blizzard Entertainment, released under the free-to-play model. Originally subtitled Heroes of Warcraft, Hearthstone builds upon the existing lore of the Warcraft series by using the same elements, characters, and relics. The game is available on the Windows, macOS, iOS and Android platforms, featuring cross-platform play. It has been a critical and commercial success, with Blizzard reporting more than 100 million Hearthstone players as of November 2018, and the game has become popular as an esport, with cash prize tournaments hosted by Blizzard and other organizers.

The game is a turn-based card game between two opponents, using constructed decks of 30 cards along with a selected hero with a unique power. Players use their limited mana crystals to play abilities or summon minions to attack the opponent, with the goal of destroying the opponent's hero. Winning matches and completing quests earn in-game gold, rewards in the form of new cards, and other in-game prizes. Players can then buy packs of new cards through gold or microtransactions to customize and improve their decks. The game features several modes of play, including casual and ranked matches, drafted arena battles, and single-player adventures. New content for the game involves the addition of new card sets and gameplay, taking the form of expansion packs.

In contrast to other games developed by Blizzard, Hearthstone was an experimental game developed by a smaller team based on the appreciation of collectible card games at the company. The game was designed to avoid the pitfalls of other digital collectible card games by eliminating any possible plays from an opponent during a player's turn and by replicating the feel of a physical card game within the game's user interface. Many of the concepts as well as art assets were based on those previously published in the physical World of Warcraft Trading Card Game.

Set within the Warcraft universe, Hearthstone is a digital-only, turn-based collectible card game which pits two opponents against each other. Players select a hero from one of eleven classes. All classes have unique cards and abilities, known as hero powers, which help define class archetypes. Each player uses a deck of cards from their collection with the end goal being to reduce the opponent's health to zero.

There are five different types of cards: minions, spells, weapons, hero cards and locations. These cards are ordered by rarity, with Legendary cards being the rarest, followed by Epic, Rare, Common, and Free. Blizzard releases expansions of additional cards every four months, as well as smaller mini-sets between expansions, to increase the variety in the metagame. The game uses a freemium model of revenue, meaning players can play for free or pay to acquire additional card packs or content.

Unlike other card games such as Magic: The Gathering, Hearthstone was designed to speed up play by eliminating any manual reactions from the opposing player during a player's turn, and setting a timer for each player's turn. During a turn, players play cards from their hand using "mana", a budget each player must abide by which increases by one each turn with a maximum of ten, and with cards having various mana costs. This invokes strategy as the player must plan ahead, taking into account what cards can and cannot be played.

Most playable cards can be classed as minions or as spells. Minions will be placed directly onto the board after being played and may carry special effects like Charge or Deathrattle, allowing the minion to attack instantly or making the minion do something special upon death, respectively. Spells have distinctive effects and affect the board in various ways.

Cards can be obtained through opening card packs or by crafting them with arcane dust, earned from destroying unwanted cards or earned in the Arena.