Brand new GameBoy Advance(GBA)/GameBoy Advance SP(GBA SP) link cable.
Will work with any Gameboy Advance or Gameboy Advance SP.

This cable is all you need to to link up to 4 GBA/GBA SP consoles together, so you can play with or against your friends.
You can also exhange data(eg: saved games) between consoles.

Also works fine with only 2 or 3 consoles connected.

Plugs are marked 'player 1', 'player 2', 'player 3', 'player 4'

As with any link cables, the game needs to support link cables(for example, many Pokemon games support link cables).

Works for Gameboy Advance games only, won't work for Gameboy Colour or the oldest Gameboy(black & white) games.
An easy way to tell if a game cartridge is Gameboy Colour(or older Gameboy game), is that the older cartridges are about twice the size of a Gameboy Advance cartridge - so sticks out of the Gameboy Advance by several centimetres.

Won't fit the Gameboy Micro, as they have a different socket.

Cable length: 1 metre from end-to-end, but there is a joining box in the middle - each plug has a 50cm cable leading to this box.