You can share an external hard drive wirelessly with the Airport Extreme, as well as a printer. You can print or play music through an Airport Express. Extreme supports the 802.11a/b/g and draft-n wifi protocols, whereas the Express supports 802.11g and draft-n only. The Extreme is a wireless router, meaning you can share a connection between wired devices that are plugged into it. It has 1 ethernet in and 3 ethernet out ports. The Express only has 1 ethernet port, that can function either as in or out, and is not meant to be a primary router. The two work beautifully together, with the Extreme acting as the base station connected to your modem, with the Express acting as a bridge, and it can share its connection through ethernet. This is how I got my Xbox online for half the price, and with lots of perks. The main difference, basically, is the ethernet ports. What kind of application were you looking for? A simple home wireless network? Remote printing or storage? That can help you make a better choice.