N400

N400 or N-400 may refer to:
 * N400 (neuroscience), an event-related potential component elicited by meaningful stimuli (words, pictures, etc.)
 * N-400 road (Spain), a highway connecting Toledo to Cuenca
 * Honda N400, a car similar to the Honda N360
 * Samsung N400, a mobile phone by Samsung
 * Form N-400, United States Citizenship and Immigration Services application for naturalization
 * A variant of the Aston Martin V8 Vantage car