Multiplayer is a feature in the Animal Crossing series that allows players to interact with each other in various forms, the most common being visiting other players' towns.
In Animal Crossing
In Animal Crossing, up to four players can live in a town, with each having their own house.
Visiting other towns
The player can talk to Porter at the Train Station to visit the town in Memory Card Slot B. Since this must be done on one console, the resident of the town in Slot B cannot play alongside the visitor.
In Wild World and City Folk
In Animal Crossing: Wild World, like in Animal Crossing, up to four players can live in a single town. However, players now live in the same house, likely due to the smaller town size. In Animal Crossing: City Folk, since the towns are larger than in Wild World, players live in separate houses again.
In Wild World and City Folk, if the player talks to Copper at the checkpoint, they can receive a 12-digit Friend Code. If this code is entered into another player's game, they can become friends. Friends can visit each other's towns and send each other letters over the Internet.
Tag Mode (known as Contact Mode in PAL regions), is a mode exclusive to Wild World that allows players to interact wirelessly. While the game is in Tag Mode, coming within range of another person who also has their game in Tag Mode will allow both to swap Notes in Bottles which have been let out to sea, as well as trade constellations and villagers.
Visiting other towns
In Wild World and City Folk, the player can talk to Copper at the checkpoint to either visit someone else's town or to open the checkpoint to allow other players into their town by telling him "I wanna go out!" or "Invite guests" respectively. Up to four players can be in a town at one time. Players can chat via an in-game keyboard, or, in City Folk only, via the Wii Speak accessory.
Local Wireless multiplayer is only available in Wild World. After telling Copper "I wanna go out!", the player will be given the option between local and online play. If local is selected the game will search for nearby Nintendo DS systems with their checkpoint open, and, if one is found, the player will visit that town. Up to four players can play in a single town via local wireless, and all players must have a copy of the game.
If online play is selected when talking to Copper, the player was able to visit the town of someone on their Friends List via the Nintendo Wi-Fi Connection. Since the Nintendo Wi-Fi Connection was discontinued on May 20th, 2014, online play is no longer possible in Wild World and City Folk.
In New Leaf
Like in previous games, up to four players can live in one town. They each have their own house, and only the first player to move in is the mayor. Therefore, other players cannot do mayoral duties such as building Public Works Projects or enacting ordinances. All players can give Bells towards the projects, however.
Friends from the player's Nintendo 3DS Friends List who also have played New Leaf will appear in the player's in-game Friends List. Like in previous games, friends can visit each other's towns over the Internet and send each other letters.
Visiting other towns
Up to four players can play in a single town via local wireless. All players must have a copy of the game.
Players can visit friends' towns over the Internet. If Parental Controls are enabled on the Nintendo 3DS, the player will not be able to visit other players' towns online or have online visitors.
Once the Dream Suite is built, the player can share a dream of their town for others to visit over the Internet. The dream acts as a saved state of the player's town at the time of sharing, and it must be updated manually.
Happy Home Showcase
The Happy Home Showcase allows players to meet and visit the houses of players that they have met over StreetPass.
In New Horizons
In Animal Crossing: New Horizons, this is the first game where up to eight players can live on one island, and they each have their own house once again.
For the first time in the series, up to four players can play simultaneously on a single console. The players must be residents of the island. A player can use the Call Resident app on their NookPhone to call up other residents on the island. This will start a mode called Local Co-Op, where a player who called the others is assigned the role of "leader" while the others are known as "followers". The leader can be switched by shaking the Joy-Con or Pro Controller. Any bugs or fish caught by the followers will be sent to the Recycling Bin at the Resident Services. If one of the followers are switched to a leader and end the session, they will be able to play on their own profile without having to close the game and switch profiles.
Friends from the player's Nintendo Switch Friends List who also have played New Horizons will appear in the player's in-game Friends List. Like in previous games, friends can visit each other's islands over the Internet and send each other letters. A player must at least visit their friend's island or have their friend come to that player's island in order to send letters, they can also mark each other as best friends if conditions have been met and can send messages via the Best Friends app on NookPhone. This also marks the first game where a player's friend cannot modify the island with a Shovel or Axe unless they are registered as Best Friend.
Visiting other islands
Up to eight players can play on a single island via local wireless. All players must own a copy of the game. Additionally, the host does not need to mark them as Best Friend in order to modify the island.
Players can visit friends' islands over the Internet, or they can enter a one-time use Dodo Code to visit the island of someone not on their Friends List, including dreams. All methods require a paid Nintendo Switch Online membership.