E numbers are codes for substances that are permitted to be used as food additives for use within the European Union and Switzerland. The "E" stands for "Europe". They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority.

The number is an important mathematical constant that is the base of the natural logarithm. It is approximately equal to 2.71828, and is the limit of as approaches infinity, an expression that arises in the study of compound interest. It can also be calculated as the sum of the infinite series