The Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter lets you connect Thunderbolt and Thunderbolt 2 devices — external hard drives and Thunderbolt displays, for example — to any of the Thunderbolt 3 (USB-C) ports on your MacBook Pro. As a bidirectional adapter, it can also connect new Thunderbolt 3 devices to a Mac with a Thunderbolt or Thunderbolt 2 port.*
*Requires macOS Sierra.
IMPORTANT NOTE: Althought Thunderbolt 2 and Mini DisplayPort use the same connector, the Thunderbolt 3 to Thunderbolt 2 Adapter does NOT support Mini DisplayPort displays.
If you have a computer with Thunderbolt 3 and wish to use a display with Mini DisplayPort, you will need to use a USB-C to DVI adapter (or VGA or HDMI). Most Mini DisplayPort displays also include one or more of these other display connections so you will need to connect via this other video connection, not the Mini DisplayPort.