What accessory lets Pokémon Red and Blue players trade and battle between Game Boy systems?

The Game Link Cable lets Pokémon Red and Blue players trade and battle between Game Boy systems.

Each player connects a Game Boy cartridge to another system with the cable, then uses the game's communication features to exchange Pokémon or fight. This hardware connection made cooperation and competition central to the original Pokémon experience.

Trading was especially important because Red and Blue contained version-exclusive Pokémon. A player could not complete the original collection using only one version without exchanging creatures with another game.

The Game Link Cable is sometimes confused with later Nintendo accessories. The Transfer Pak connected Game Boy cartridges to the Nintendo 64, while the Wireless Adapter was introduced for later Game Boy Advance games.