The Nintendo Wi-Fi Connection (WFC) is a feature on Mario Kart DS that enables you to race against people in your state or around the world, including your friends.

Basic info:
- Your friend code is located (starting in the Nintendo WFC Menu) in "Friend Code">"Confirm Friend Code".
- To battle against friends you must first exchange friend codes then go to "Nintendo WFC Match" connect to the internet and select "Friends" by touching the left or right yellow arrows.
- To battle with another person you must go to "Nintendo WFC Match" and select either "Regional" or "Worldwide"