Flappy Bird is a 2013 casual mobile game developed by Vietnamese video game artist and programmer Dong Nguyen (Vietnamese: Nguyễn Hà Đông), under his game development company .Gears. The game is a side-scroller where the player controls a bird, Faby, attempting to fly between columns of green pipes without hitting them. The player's score is determined by the number of pipes they fly through. Nguyen created the game over a period of several days, using the bird from a cancelled game made in 2012.

The game was released in May 2013 but received a sudden spike in popularity in early 2014, becoming a sleeper hit. Flappy Bird received poor reviews from some critics, who criticized its high level of difficulty and alleged plagiarism in graphics and game mechanics, while other reviewers found it addictive. At the end of January 2014, it was the most downloaded free game in the App Store for iOS. During this period, its developer said that Flappy Bird was earning $50,000 a day from in-app advertisements as well as sales.

Flappy Bird was removed from both the App Store and Google Play on February 10, 2014, with Nguyen claiming that he felt guilty over what he considered to be the game's addictive nature and overusage. Its popularity and sudden removal caused phones with the game installed before its removal to be put up for sale for high prices over the Internet. Clones of Flappy Bird became popular on the App Store after the original app's removal, and both Apple and Google have removed games from their app stores for being too similar.

In August 2014, a revised version of Flappy Bird, called Flappy Birds Family, was released exclusively for the Amazon Fire TV. Bay Tek Games also released a licensed coin-operated Flappy Bird arcade game.

Flappy Bird is an arcade-style game in which the player controls the bird Faby, which moves persistently to the right. They are tasked with navigating Faby through pairs of pipes that have equally sized gaps placed at random heights. Faby automatically descends and only ascends when the player taps the touchscreen. Each successful pass through a pair of pipes awards the player one point. Colliding with a pipe or the ground ends the gameplay. During the game over screen, the player is awarded a bronze medal if they reach ten or more points, a silver medal from twenty points, a gold medal from thirty points, and a platinum medal from forty points.

Dong Nguyen was a student of HUST (Hanoi University of Science & Technology), grew up in Vạn Phúc, a village near Hanoi. He discovered video games by playing Super Mario Bros. as a child and began coding his own at age 16. At 19, while studying programming at a local university, he won an internship at Punch Entertainment, one of the few video game companies in Vietnam. While using the iPhone, he found that its most popular games such as Angry Birds were too complicated, and wanted to make a simpler game for people who are "always on the move".

Flappy Bird was created and developed by Nguyen in two to three days. The game was originally called "Flap Flap". The bird character, Faby, was originally designed in 2012 for a cancelled platform game. The gameplay was inspired by the act of bouncing a ping pong ball against a paddle for as long as possible. Initially the game was significantly easier than it became in the final version, but Nguyen said he found this version to be boring and subsequently tightened up the difficulty. He described the business plan of a free download with in-game advertisements as "very common in the Japanese market".

Nguyen believes that contemporary Western games are overly complex. His company, .Gears, describes its games as "heavily influenced by retro pixelated games in its golden age. Everything is pure, extremely hard and incredibly fun to play".