E400

E400 may refer to:
 * Alginic acid
 * Alexander Dennis Enviro400, a twin-axle, low-floor double-decker bus
 * Eclipse 400, a light jet aircraft
 * Acer beTouch E400, a smartphone
 * Mercedes-Benz E400 Hybrid, an automobile
 * One of the locomotives of Taiwan Railways Administration
 * GV-E400 series, a DEMU train type on order by JR East in Japan