With the Thunderbolt 3 (USB-C) to Thunderbolt 2 adapter you can connect Thunderbolt and Thunderbolt 2 devices – such as external hard drives or Thunderbolt docks – to any Thunderbolt 3 (USB-C) port on your MacBook Pro.

The bidirectional adapter can also connect new Thunderbolt 3 devices to a Mac with a Thunderbolt or Thunderbolt 2 port and macOS Sierra.

It also allows you to connect Thunderbolt-compatible displays such as the Apple Thunderbolt Display and LG Thunderbolt 2 displays to any Thunderbolt 3 (USB-C) port on your MacBook Pro. If you use the adapter with an Apple Thunderbolt Display, you will need a separate power connection as the display cannot draw power from the adapter.
Note: This adapter does not support DisplayPort displays such as the Apple LED Cinema Display or DisplayPort and Mini DisplayPort displays from other manufacturers. For more information, see the Apple Support page for the Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter.