Tomodachi Collection is a 2009 social simulation video game developed and published by Nintendo for the Nintendo DS. The game follows the daily interactions between interactable Miis who reside on an island overseen by the player as they build relationships and solve problems.

The game was formulated by junior Nintendo employees in October 2005 as an imitation of the Nintendo-published video game Tottoko Hamtaro: Tomodachi Daisakusen Dechu (2000). Titled Otona no Onna no Uranai Techō, the avatars featured in the character-creation system served as the progenitors for what would become the Miis. With suggestions from Satoru Iwata and Shigeru Miyamoto, the team was reassigned to implement the Miis onto the Wii console, during which the game's production was put on hold. Following the Wii's release, the project restarted as Tomodachi Collection around April 2007. Developers sought to create entertaining gameplay that emphasized the human-like characteristics of the Miis, whom players were incentivized to create in the image of their real-world friends and family.

Tomodachi Collection released solely in Japan on June 18, 2009. It garnered contemporary and retrospective praise for its unconventional tone and presentation. Tomodachi Collection was a domestic commercial success, selling 3.2 million copies by March 31, 2010, making it one of the best-selling DS games.

Following unrealized plans to localize the title overseas, Tomodachi Collection was followed up by the internationally-released sequel Tomodachi Life for the Nintendo 3DS in 2013. Another sequel, Tomodachi Life: Living the Dream, released on the Nintendo Switch worldwide, on April 16, 2026.

Tomodachi Collection is a social simulation game featuring Miis, user-customizable avatars, populating an apartment complex located on an island. To add Miis, the player can transfer existing Miis directly from their Wii to their Nintendo DS, import Miis from other players' DS consoles via wireless local connectivity, or create new ones from scratch using the in-game Mii Maker. In either case, the player manually modifies their Miis' appearance and personality. There are four temperament categories Miis can occupy, which, together with their assigned date of birth, conjures an "ideal job" that matches them. The Miis audibly speak through computer-generated voice synthesis. A maximum of 100 Miis can live on the island at once.

After creation, Miis request assistance with particular problems at random intervals, signified by the presence of a thought bubble. These issues include asking for food, clothing, guidance on prospective relationships, and player participation in short minigames. Satisfying their needs advances their level, a numeric progression system, upon which the player can gift them new clothes, interior designs for their apartment, personalized catchphrases, or songs for them to perform. Completing minigames awards the player with valuables that can be exchanged for in-game currency. The player can optionally eavesdrop on the Miis' dreams while they sleep.

Tomodachi Collection has no end condition, the player's only goal being to maintain their Miis' satisfaction and passively observe their actions. Outside of the player's direct influence, the Miis regularly interact with each other, establishing friendships and occasional conflict. If two friendly Miis share romantic attraction, one can confess their love to the other; if the confession is successful, the two are paired as a couple. Marriage can occur following additional interactions. As the player continuously appeases the Miis, new venues and shops on the island become unlocked. These include a Career Hall where jobs are formally assigned to Miis, a Compatibility Tester that gauges two Miis' likelihood of friendship, and a vendor for purchasing apartment interiors. An in-universe news broadcast occurs regularly to inform the player of recent events on the island. Time-sensitive events held by the Miis also take place in the island's fountain. Time on the island passes parallel to that set on the player's console, even when the console is powered off.

Tomodachi Collection was first conceptualized around October 2005 by a small team of junior employees at Nintendo SPD. Its premise was inspired by the fortune-telling video game Tottoko Hamtaro: Tomodachi Daisakusen Dechu (2000) published by Nintendo for the Game Boy Color in Japan. Tottoko Hamtaro, whose core audience were young girls, had users register a list of virtual profiles of close friends to measure compatability and generate predictions about their day-to-day lives. Producer Yoshio Sakamoto recounted that some female employees requested a derivative version of Tottoko Hamtaro geared to older women be made; he stated, "I also thought the same thing, and the thought stayed with me. After that I was in a team made up of all new people and we were relatively free to do what we wanted." With the dual purpose of elevating the Nintendo DS' overall appeal to women, the project became tentatively known as Otona no Onna no Uranai Techō (大人のオンナの占い手帳, lit. 'Women's Fortune Telling Pocket Notebook'). Initially only including textual information about personal names and birthdays, the team resolved to add a three-dimensional character creation mechanism. This system—inspired by the Japanese game fukuwarai, which involves assembling a face using disembodied parts—had players manually combine selected face elements to create caricatures of real-world people. The abilities to rotate, resize, and reposition facial features were added, enhancing the character-creator's accuracy.