Kantai Collection (Japanese: 艦隊これくしょん, Hepburn: Kantai Korekushon; lit. 'Fleet Collection'), abbreviated as KanColle (艦これ, KanKore), is a Japanese free-to-play web browser game developed by Kadokawa Games and published by DMM.com.

The central theme of the game is the representation of World War II warships personified as teenage girls and young adult women with personality characteristics reflecting the history of each ship. All of the featured ships were originally Japanese, but ships from other nations, like America and Germany, have also been implemented as the game has developed. Gameplay involves all aspects of naval warfare, including not only combat but also maintenance, repair, upgrading, resupply, morale, logistics as well as mission planning.

The game was launched on April 23, 2013. The game is available in Japan only and as of April 2015 has 3 million registered players. An Android client of the original game was released in 2016. The game has developed into a much larger media franchise; various media including multiple manga series and light novels have been released, in addition to an officially licensed tabletop role-playing game. A PlayStation Vita game was released in February 2016, and an anime television series aired its first anime from January to March 2015, with an animated film released in November 2016, and a second anime that premiered in November 2022.

The gameplay is centered upon building squadrons composed of individual characters, "ship girls" (艦娘, kanmusu), represented as cards with different attributes, and then sending said squadrons out on missions. The player takes on the role of an admiral (提督, teitoku) and organizes their fleets in battle in order to win. Combat is largely automated, and manual actions by the player include micromanagement such as building and repairing. The player can organize up to four different fleets.

The player progresses through the game by advancing through maps, gaining experience points through grinding, obtaining new ship girls whilst repairing and resupplying existing ones, and fulfilling quests to obtain resources. New equipment can be crafted, allowing the ship girls to equip different armaments depending on the situation. Acquisition of new kanmusu by the player can occur via drops on map or via crafting, and is heavily RNG-based; randomization is also a key component of the battle mechanism, map progression and equipment development. Construction, resupply and repair of ships is reliant upon four types of resources, namely fuel, ammunition, steel and bauxite; these supplies will gradually increase automatically as time passes. Players can choose to engage in expeditions, sorties, and quests to further increase their supplies as well.

Ships can be customised through the addition of various equipment within their empty slots, which add attribute bonuses and even provide special effects in some cases; such equipment include naval guns, anti-aircraft guns, torpedoes, torpedo bombers, dive bombers, fighter aircraft, seaplanes, recon planes, radars, steam turbines, special artillery shells, depth charges, sonars, drum canisters, searchlights and anti-torpedo bulges. The effectiveness of ships in combat depend on its attribute parameters, namely hitpoints, armour, evasion, aircraft capacity, speed, attack range, firepower, torpedo, anti-air, anti-submarine, line-of-sight, and luck.

Kanmusu are capable of becoming stronger as they gain experience and level up after battles, and can also be remodeled into more advanced models once they reach a certain level. Unwanted kanmusu can also be "fed" to other kanmusu through a process known as "modernization" (近代化改修, kindaika kaishu), which grants attribute bonuses to one ship in exchange for losing another. Ships can become fatigued once it accumulates after sorties; fatigued ships have decreased attributes, whilst sparkling ships have increased attributes. Fatigue can be alleviated by allowing ships some time to rest, or by recovering the fleet's morale using Japanese food supply ship Mamiya. As ships become damaged, their icons begin to blow off smoke and their clothing become visually torn and battered; in the event when a ship's durability drops down to zero, it is considered sunk, and the player will lose the ship girl. Players cannot resurrect ship girls that have been lost unless they are in possession of an emergency repair item, and are only able to re-train ships that have been lost from scratch.

Whilst the game is free-to-play, special premium bonuses can be obtained through prepaid game money and credit card microtransactions, such as repair dock expansions, home shipyard furniture tokens, ship possession limit increases, and special consumable items. Although each ship in the game has an experience level cap of Lv.99, the player is able to obtain the "marriage papers and ring" item with a monetary purchase priced at 700 yen or via a one-time special quest, which allows the player to "marry" the girl, thereby breaking the original level cap and allowing a new maximum of Lv.175, in addition to other perks such as stat boosts and decreased operating costs; this process can be repeated as many times as the player wishes, and there is no limit to the number of girls that can be "married".