A UN (United Nations) number is used by the Department of Transportation (DOT) as a method of identification and classification of products for shipping purposes.

UN numbers are different from the hazard class or division designations used by DOT (for example, 1.1, 1.2, 1.3, 1.4, and 1.5). ATF regulations in 27 CFR Part 555 also use UN numbers to help identify certain explosives.

[27 CFR 555.11]