The Nintendo Wi-Fi USB Connector is an accessory, developed jointly by Nintendo and Buffalo Technology, which allows Nintendo DSi and Nintendo 3DS and Wii users without a Wi-Fi connection or compatible Wi-Fi network to establish one via a broadband-connected PC. Inserted into the host PC's USB port, the connector functions with Nintendo DS, Wii, DSi, 3DS permitting the user to connect to the Internet to play Nintendo Wi-Fi Connection games and various other online functionality. The product was the best selling Nintendo accessory to date, according to the official Nintendo site on 15 November 2007, but was discontinued in the same month until further notice. On September 8, 2008, Nintendo announced the Nintendo Wi-Fi Network Adapter, an 802.11g wireless router/bridge which serves a similar purpose.

FunctionalityThe Nintendo Wi-Fi USB Connector is a rebranded Buffalo WLI-U2-KG54-YB (Although this is often confused for the Buffalo WLI-U2-KG54-AI - the two adapters are almost identical, and only differ in that the latter features flash memory to allow for auto installation) which is based on the Ralink RT2570 chipset and as such is different from most other Wi-Fi adapters in that it can operate as a software access point (also referred to as a soft AP). Few adapters can do this under Windows, as at the time of the Nintendo Wi-Fi USB Connector's release, Windows lacked both the software necessary to configure a soft AP and capable drivers for natively supported hardware. By bundling a soft AP compatible device with their own proprietary software, Nintendo was able to overcome this and at the same time greatly simplify the otherwise complicated process of putting a supported device into soft AP mode, configuring it, and routing Internet traffic over it.

In addition, a number of community developed tools and drivers exist which expand the functionality of the Nintendo Wi-Fi USB Connector beyond its initial design. While not officially supported by Nintendo, the USB Connector can function as a standard wireless adapter by using modified Ralink or Buffalo Technology drivers, and can be used to send official game demos and homebrew software to the Nintendo DS through the Wireless Multi Boot (WMB) protocol.