The Transfer Pak is a Nintendo 64 accessory that allows the transfer of data from a Game Boy game cartridge. The Transfer Pak fits onto the expansion port of the Nintendo 64 controller. The hardware is limited to the transfer of data; it is incapable of playing Game Boy video games on the Nintendo 64.

The Transfer Pak was included with the game Pokémon Stadium in North America, as the game's main feature was importing Pokémon from Pokémon Red Version, Pokémon Blue Version and Pokémon Yellow Version: Special Pikachu Edition. Pokémon Stadium included a feature called "GB Tower" for playing Pokémon Red, Blue, and Yellow on the Nintendo 64 via a built-in Game Boy emulator (which included the unlockable "Doduo" and "Dodrio" modes which would speed up the game's processor by factors of two and three, respectively).

The Transfer Pak was also used for connectivity between Mario Golf 64, and Mario Golf on the Game Boy Color. Kid, Sherry, Azaelea, and Joe from the Game Boy Color version could be transferred to the Nintendo 64 version. In later versions of a data transfer, this was replaced by the Nintendo WFC Transfer Utility (DS family), for the second time by the Pikmin picking up DSi or 3DS data and moving it (DSi to 3DS or 3DS to 3DS XL), and for the final time by the Pikmin carrying data across the land and onto and odd ship, then to the memory core (Wii to Wii U).