No, the Asus RT-AC66U is not a modem. It is a wireless router. A modem is a device that connects to your internet service provider (ISP) and allows you to access the internet, while a router is a device that allows multiple devices to connect to the internet and share that connection. The Asus RT-AC66U can be used in conjunction with a separate modem to provide wireless internet access to multiple devices in your home or office.