X40 may refer to:
Boeing X-40, test platform for the X-37 Future-X Reusable Launch Vehicle SJ X40, series of electric multiple units operated by SJ of Sweden Southern Vectis route X40, bus route on the Isle of Wight, England ThinkPad X40, laptop computer by Lenovo Bestune X40, a subcompact crossover
de:X-40 fr:X40