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,
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