2048 is a single-player sliding tile puzzle video game written by Italian web developer Gabriele Cirulli and published on GitHub. The objective of the game is to slide numbered tiles on a grid to combine them to create a tile with the number 2048; however, one can continue to play the game after reaching the goal, creating tiles with larger numbers. It was originally written in JavaScript and CSS over a weekend, and released on 9 March 2014 as free and open-source software subject to the MIT License. Versions for iOS and Android followed in May 2014.

2048 was intended to be an improved version of two other games, both of which were clones of the iOS game Threes released a month earlier. Cirulli himself described 2048 as being "conceptually similar" to Threes. The release of 2048 resulted in the rapid appearance of many similar games, akin to the flood of Flappy Bird variations from 2013. The game received generally positive reviews from critics, with it being described as "viral" and "addictive".

2048 is played on a plain 4×4 grid, with numbered tiles that slide when a player moves them using the four arrow keys. The game begins with two tiles already in the grid, having a value of either 2 or 4, and another such tile appears in a random empty space after each turn. Tiles with a value of 2 appear 90% of the time, and tiles with a value of 4 appear 10% of the time. Tiles slide as far as possible in the chosen direction until they are stopped by either another tile or the edge of the grid. If two tiles of the same number collide while moving, they will merge into a tile with the total value of the two tiles that collided. The resulting tile cannot merge with another tile again in the same move. Higher-scoring tiles emit a soft glow; the largest possible tile is 131,072.

If a move causes three consecutive tiles of the same value to slide together, only the two tiles farthest along the direction of motion will combine. If all four spaces in a row or column are filled with tiles of the same value, a move parallel to that row/column will combine the first two and last two. A scoreboard on the upper-right keeps track of the user's score. The user's score starts at zero, and is increased whenever two tiles combine, by the value of the new tile.

The game is won when a tile with a value of 2048 appears on the board. Players can continue beyond that to reach higher scores. When the player has no legal moves (there are no empty spaces and no adjacent tiles with the same value), the game ends.

Strategies in 2048 include keeping the largest tile in a specific corner with other large tiles filling the row (either vertically or horizontally). If the row remains filled, the player can then move in three different directions while still keeping the largest tile in the preferred corner. As a general rule, no small tiles should be separated from other small tiles by a large tile.