The Game Link Cable let players exchange Pokémon between two original Game Boy cartridges. Pokémon Red and Green were designed around this accessory, making trading a central feature rather than an optional novelty.
Each game version contained Pokémon unavailable in the other, so completing the Pokédex required connecting two systems and trading with another player. The same cable also supported battles, allowing trainers to test teams outside the single-player adventure. This social design helped distinguish Pokémon from many role-playing games of its era.
The Game Link Cable was a physical Nintendo accessory for Game Boy, Game Boy Pocket and related systems. Later Pokémon games replaced cable trading with infrared communication, wireless adapters or internet services. The Transfer Pak, by contrast, connected Game Boy cartridges to Nintendo 64 games and was not the original Red-and-Green trading method.