With this Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter, you can connect Thunderbolt (2) devices to your new MacBook with USB-C/Thunderbolt 3 port. Think external hard drives or an extra screen with Thunderbolt or Thunderbolt 2 connector, for example. Because it's bidirectional, you can also use this adapter to connect new Thunderbolt 3 devices to an (older) iMac or MacBook with a Thunderbolt or Thunderbolt 2 port.