Little Busters! (リトルバスターズ!, Ritoru Basutāzu!) is a Japanese visual novel developed by Key. It was released on July 27, 2007 for Windows PCs and is rated for all ages. Little Busters! is Key's sixth game, along with other titles such as Kanon, Air, and Clannad. An adult version of the game titled Little Busters! Ecstasy was released on July 25, 2008 for Windows, unlike Kanon and Air, which were first released with adult content and then had later versions with such content removed. Ecstasy was later ported to the PlayStation 2, PlayStation Portable, PlayStation Vita, PlayStation 3, and Nintendo Switch with the adult content removed under the title Little Busters! Converted Edition. An English version for Windows was released on Steam in 2017. The story follows a group of childhood friends (Riki Naoe, Rin Natsume, Kyousuke Natsume, Masato Inohara and Kengo Miyazawa) now attending high school called the Little Busters, as they decide to form a baseball team. Riki, who is diagnosed with narcolepsy, is tasked to recruit more girls in preparation for a baseball game, and he bonds with each of them on account of their internal conflicts. Meanwhile, Rin gets mysterious letters from her cat Lennon to complete various tasks to learn the "secret to this world".

The gameplay in Little Busters! follows a branching plot line which offers pre-determined scenarios with courses of interaction, and focuses on the appeal of the six female main characters by the player character, which increases to nine in Ecstasy. There are additional minigames added into the gameplay, such as battle sequences that resemble fighting games or baseball batting practice, which serve to give the characters experience, obtain accessories to use during battle, and improve their statistics. Both Little Busters! and Ecstasy ranked as the best-selling PC game sold in Japan for the time of their release, and Ecstasy would go on to sell over 100,000 units. Key went on to produce an adult spin-off called Kud Wafter in June 2010, which expanded on the scenario of Kudryavka Noumi, one of the heroines from Little Busters! and Ecstasy.

There have been 14 manga adaptations based on Little Busters! and Ecstasy published by ASCII Media Works, Kadokawa Shoten and Ichijinsha. Comic anthologies, light novels and art books were also published, as were several music albums. There have been two Internet radio shows hosted by the voice actors of Rin and Kyousuke Natsume and Kudryavka Noumi. J.C.Staff produced two anime television series and an original video animation series between 2012 and 2014.

Little Busters! is a romance visual novel in which the player assumes the role of Riki Naoe. Much of its gameplay is spent on reading the story's narrative and dialogue. The text in the game is accompanied by character sprites, which represent who Riki is talking to, over background art. Throughout the game, the player encounters CG artwork at certain points in the story, which take the place of the background art and character sprites. When the game is completed at least once, a gallery of the viewed CGs and played background music becomes available on the game's title screen. Little Busters! follows a branching plot line with multiple endings, and depending on the decisions that the player makes during the game, the plot will progress in a specific direction.

There are seven main plot lines that the player will have the chance to experience. Throughout gameplay, the player is given multiple options to choose from, and text progression pauses at these points until a choice is made. To view all plot lines in their entirety, the player will have to replay the game multiple times and make different choices to further the plot to an alternate direction. When first playing the game, the scenarios for all six heroines are available. Once a scenario for any one heroine is completed, that scenario will be unavailable in the next play through because the last choice that will ultimately lead to that heroine's scenario becomes unavailable for players to choose. After the completion of these six routes, the final scenario called Refrain is made available, which serves to bring everything to a definite conclusion and answers questions brought up throughout the normal gameplay. Completing Refrain makes available all the heroine's scenarios that were previously made inaccessible during gameplay so that the player can revisit the scenarios again, along with some extra decision points that were previously unavailable.

Throughout gameplay, the player encounters various minigames, which range from simple to more complex. The first type of minigame encountered is a battle sequence that resembles a fighting game, but no interaction from the player is required to fight. These recurring battle sequences represent when the members of the Little Busters get into physical fights with either each other or with others. Each member of the fight has a set of statistics attributed to them (which includes strength, stamina, agility, reflex, concentration, judgment, and luck) along with a life bar to keep track of how many hit points a fighter has left. The maximum number of hit points is determined by the given fighter's stamina rating. Weapons may be used along with any accessories the fighter has in their possession, and these items may be exchanged with other characters. Another recurring minigame involves the player being able to play baseball batting practice with members of the Little Busters. The player, as Riki, controls his position and when to swing the bat.

The Little Busters will also participate in missions to accomplish some goal, and a mission will either be completed or failed depending on the choices of the player. These missions are connected with the battle sequences and batting practice in that they serve to give the characters experience, obtain accessories to use during fights, and improve their statistics. However, these missions do not affect the main plot in any way—the player even has the choice to turn off most of the minigames so that the player may focus on the main plot, including the battle sequences and batting practice. The first time that the game is played, Rin's statistics are weak compared to other characters. However, when the player completes several heroine's routes, Rin's and Riki's statistics will start out higher than before when the player starts a new game, allowing Rin and Riki to stand a better chance against opponents with higher statistics. The statistics of the Little Busters members are shown in a ranking system from highest to lowest in overall statistics.

Despite Little Busters! having a rating for all ages, there is an ample amount of CG artwork featuring the female characters in risqué situations, though never to the point to be considered sexual in nature. This is in stark contrast to Key's previous titles Clannad and Planetarian: The Reverie of a Little Planet that also have ratings for all ages, but those titles contain no such risqué situations or even any fan service.